Freenet Decentralized Application Builder

Build decentralized applications on Freenet following the architecture patterns established in River (decentralized chat).

How Freenet Applications Work

Freenet is a platform for building decentralized applications that run without centralized servers. Apps store and exchange data through a global, peer-to-peer Key-Value Store shared by every Freenet node.

The keys in that store are not arbitrary strings — they're derived from small pieces of WebAssembly called contracts that define how each value is allowed to change. The next two sections introduce the kinds of components that make up a Freenet app, then explain exactly how contract keys are formed and why that makes the system trustless.

The Three Kinds of Components in a Freenet App

A Freenet app is built from three kinds of components — contracts, delegates, and a UI. Most non-trivial apps have multiple contracts and multiple delegates, each handling a different concern.

1. Contracts (Network State)

A Freenet app typically has one or more contracts, each defining a different kind of shared state. River has a single room contract today, but a more complex app might have several (e.g. rooms, user profiles, invitations, search indexes), and each one is a separate contract crate that compiles to its own WASM.

• Role: Closer to a database table than a database. The contract WASM defines the schema (state shape) and the rules for validation and merging. Each instance of the contract — there can be many — behaves like an independent row in that table, so a chat app can have thousands of "room" rows all governed by the same room-contract WASM. (How rows are addressed is covered in How Contract Keys Work below.)
• Location: Runs on the public network (untrusted peers).
• Functionality:
  • Defines what state is valid
  • Defines how state can be modified (validate / update / summarize / delta)
• State: Holds the actual application data for that instance (arbitrary bytes).
• Constraint: Cannot hold private keys or secrets — all state is public unless encrypted by the client.

2. Delegates (Local Trust Zone)

A Freenet app may have one or more delegates, each handling a different local responsibility — key management, secret storage, background sync, notifications, and so on. Delegates are the local counterpart to contracts: where contracts hold shared state on the network, delegates hold private state on the user's device.

• Role: Trusted middleware between the user and the network.
• Location: Runs locally on the user's device, inside the Freenet kernel.
• Functionality:
  • Trust Zone: Safely stores secrets, private keys, and user data
  • Computation: Performs signing, encryption, and complex logic before publishing to the network
  • Background Tasks: Can run continuously to monitor contracts or handle notifications even when the UI is closed

3. The User Interface (Frontend)

A single UI typically talks to all of an app's contracts and delegates.

• Role: Interaction layer for the user
• Location: Web Browser (SPA) or native app
• Functionality:
  • Connects to the local Freenet Kernel via WebSocket/HTTP
  • Built using standard web frameworks (Dioxus, React, Vue, etc.)
  • Agnostic to underlying P2P network complexity
• How it is published and addressed: the UI ships as the state of a web container contract — a generic, pre-built contract whose params are your 32-byte publisher key. Because neither key input contains your UI, your webapp has one permanent URL and is upgraded in place: fdev website update publishes v2 to the same address users bookmarked. Do not design around a rotating URL, and do not build a redirect contract to work around one. See references/web-container-contract.md.

"Native app" above means desktop. Freenet does not currently support running a full node on mobile devices. Do not recommend or generate a production mobile wrapper without clearly warning about likely bandwidth, battery, thermal, CPU, and background-execution problems. Treat any such work as experimental, require explicit resource measurements before calling it viable, and do not represent it as an official Freenet client without approval from the Freenet Project.

How Contract Keys Work (and Why Freenet is Trustless)

Now that contracts have been introduced, here's how they're addressed in the network.

The key for a piece of data is derived from the cryptographic hash of the contract's WebAssembly (WASM) code, combined with a set of contract parameters that identify a specific instance.

• The WASM hash ties the identity of the data to its logic — change the code, and the key changes.
• The parameters distinguish independent instances of the same contract code. Tying back to the database-table analogy: the WASM is the table schema, and each parametrized instance is a row with its own key and its own state.
• This is what makes the network "trustless" — you don't have to trust the peer that holds the data, because the data is self-verifying against the contract code referenced in the key.

Data Synchronization & Consistency

Freenet solves "Eventual Consistency" using a specific mathematical requirement:

Join-semilattice: The function that merges updates must be associative, commutative and idempotent.

• Order Independent: It shouldn't matter what order updates arrive in
• If Peer A merges Update X then Y, and Peer B merges Update Y then X, they must end up with the same result
• Redelivery-safe: merge(A, A) == A. Delivery is at-least-once, so the same update will arrive twice — after a retry, a re-subscribe, or anti-entropy. A merge that changes the state on re-application never settles. This is the requirement most often missed; see references/contract-patterns.md → "Merge Law Requirements" for why identity is not the same thing, and for the property tests.

A contract must not read the host clock. freenet_stdlib::time::now() is deprecated for contracts as of freenet-core v0.2.132. The merge has to be a function of its inputs — that requirement is why replicas converge — so a merge that reads the wall clock isn't merely breaking the laws above; they stop being well-formed statements about it. Two peers eleven minutes apart can produce different states from the same delta and neither is wrong. Today a node logs a warning on loading such a contract and fdev verify-merge reports a host_clock_import diagnostic; nothing traps yet, but the call is staged to trap (freenet-core#5465), and when it does the failure is per-call rather than a refusal to load, so no re-key is needed. Carry a client-signed timestamp in state and enforce only monotonicity instead — with clear eyes about what that costs, since a client timestamp is an untrusted hint and can't do anti-grief. Delegates are unaffected. See references/state-authorization-patterns.md → "Time Handling".

Check your contract against all of this rather than trusting it:

fdev verify-merge --wasm your_contract.wasm --state s1.bin --state s2.bin

It exercises the merge laws against a real corpus, and separately reports code diagnostics — host_clock_import being the one that exists today. A code diagnostic never fails the command: it describes the code, not a law the contract broke.

Efficiency: Peers exchange Summaries (compact representations) and Deltas (patches/diffs) rather than re-downloading full state.

Requirement: get_state_delta must not ship state to a peer that already has it. When the requester's summary shows it holds everything you have, the delta carries no information, so it must not contain the state or approach the state's size. It should be a literally empty StateDelta (vec![]), which is the unambiguous "converged" answer and what freenet-scaffold produces for you; a few tens of bytes of encoding framing from serializing an all-empty struct is acceptable. What matters is delta size relative to state size: 20 bytes against a 500 KB state is fine, a state-sized delta is a broken delta mechanism that re-ships everything on every reconciliation, forever. Your summary must likewise be far smaller than your state. Core is adding a probe for contracts that get this wrong, and it currently costs the network real bandwidth. Full detail, code shapes, and a test are in references/contract-patterns.md → "The Delta to an Up-to-Date Peer".

State and summaries must serialize canonically

Use deterministic maps everywhere in state AND summaries: BTreeMap/BTreeSet, never HashMap/HashSet. Peers decide they have converged by comparing state bytes, so two peers holding the same logical state in a different byte order heal forever without ever agreeing. Canonical encoding is a platform requirement (freenet-core #5320), and the merge laws are checked on exact bytes because of it. A HashMap serializes in nondeterministic order (ciborium), so two identical states can summarize to different bytes and core's byte-level convergence check misfires — spurious heals, or missed ones. The same caution applies to any map inside whatever summarize returns.

Beyond that, make sure your state genuinely converges through summarize / delta / apply, and test that it does, rather than assuming a live broadcast reaches every peer.

Previously documented here as a live limitation, now fixed. freenet/freenet-core#4857 ("State updates permanently lost for rarely-changing fields") is CLOSED. A ContractQueueFull drop was silent, and the sender cached its own summary as the receiver's on send-Ok, so it believed the peer was current and never re-sent — leaving rarely-changing fields (config, permissions, ban lists) diverged until the ~5-minute InterestSync heartbeat happened to correct them.

The shipped fix has the queue-full receiver emit a ResyncRequest, which makes the sender clear its poisoned summary and re-send full state. It is throttled to one per (contract, peer) per 30s, because #4251 showed that one request per dropped delta amplifies into a full-state storm onto the same saturated queue; #4862 hardened it against bridge backpressure. See RESYNC_REQUEST_MIN_INTERVAL in crates/core/src/ring/interest.rs.

Do not design around multi-minute staleness on rarely-changing fields, and do not treat a ban list or permission field as needing to ride alongside a frequently-changing one. The earlier guidance to do so is retired.

Keep summaries small — it is measured, and it is expensive

Summaries are ~23.7% of all outbound bytes on the Freenet network, and the fleet-mean summary is 16,675 bytes against a protocol digest-entry size of 21 bytes (freenet-core#5153). A fat summary is not a local inefficiency: it ships to every interested peer on every ~5-minute anti-entropy heartbeat whether or not anything changed, and it sets the floor for how cheaply a peer can be brought up to date.

Every rule below is checkable in review and grounded in a measured finding from River.

1. Every summary field must be read by delta(). Grep each field name against the delta() bodies. A field nothing reads is dead weight re-sent forever.

2. A value that is only ever compared for equality must be a fixed-width digest, never the thing it fingerprints. River carried raw Ed25519 signatures in member_info purely to run >; replacing them with a 16-byte digest measured 135.27 → 28.01 bytes per entry. The DM summary still does this for a bare contains() at 66 bytes/entry — 19,803 bytes at its cap, larger than the whole rest of the summary (freenet/river#596).

3. Size a digest by who controls the colliding inputs, not by taste. If a party can grind both sides of the comparison, 64 bits is a ~2^32 birthday search — hours on commodity hardware — so use 128. If the attacker controls only one side, 64 may do. Write the threat model in the doc comment. A collision here is not a crash; it is a record that silently never propagates.

4. Assert the encoding; never derive it. The same 64 bytes cost 66 CBOR bytes as a byte string and 119 as a derived tuple — ciborium maps serialize_tuple to an array where every byte ≥ 24 costs two. River quoted 66 for a type that actually encoded at 119, and the wrong number survived an issue, a PR body, and a review. Hand-write Serialize with serialize_bytes for any fixed-size byte array, and pin it with a golden vector: one fixed input, one fixed expected digest, one fixed expected byte length. A randomised digest oracle misses byte-order bugs intermittently.

5. Measure size with realistic key values, not small integers. A FastHash(i) for small i encodes in 1-3 CBOR bytes; a real key's encodes in 9. A test built from 0..N understates the per-entry cost by ~30% and will pass review.

6. A summary should be O(1) or sub-linear in the collections it describes — or justify the linearity in writing. A flat enumeration grows without bound as your app succeeds. If you keep it linear, state the element cap that bounds it and check cap × per-entry against your budget. River's is fully linear; at 200 members × 1000 messages it measures 16,723 bytes.

7. A lossy summary is legal when apply_delta is idempotent — exploit that. K fixed buckets each holding an 8-byte digest of that bucket's contents makes the summary constant-size: measured K=16 → 145 bytes, independent of N, against 3,894 bytes for the flat form at 139 members. get_state_delta may then return a superset of the true delta, which is sound only if applying an already-held element is a no-op — verify that first. The trade is real: one changed element resends its whole bucket. It wins because summaries go out on every heartbeat while deltas fire only on change, so measure your summary-broadcast : state-change ratio before committing.

8. A capped or pruning collection needs a retention horizon in the summary. Without one, delta() is a pure set difference: the receiver prunes what it just received, neither summary changes, and the pair re-sends forever. Publish the oldest key held, only at capacity, so it strictly increases each exchange and the loop provably terminates.

9. Nothing in a summary should reveal information the recipient is not entitled to. A summary goes to more peers, more often, than state does. River's DM summary advertises every DM in the room to every member, participant or not, leaking exact DM volume.

10. A summary is a wire-format commitment: changing it re-keys the contract and strands every existing copy. Which hash, how wide, which bytes in which order, and how it serializes are all frozen at publish. Keep a registry of past generations (River keeps legacy_room_contracts.toml, 31 entries) and expect every abandoned generation to keep costing anti-entropy bandwidth indefinitely — one stranded River generation is currently doing 3,829 failed summary comparisons against zero update events (freenet-core#5158). Batch summary changes rather than shipping them one at a time.

Advanced Capabilities

• Subscriptions: Clients can subscribe to contracts and get notified of changes immediately (real-time apps)
• Contract Interoperability: Cross-contract reads are implemented and working. validate_state can return ValidateResult::RequestRelated(Vec<ContractInstanceId>); the host fetches those contracts and re-invokes with RelatedContracts populated (fetch_related_for_validation_network in crates/core/src/contract/executor/runtime/contract_ops.rs, on both the PUT and UPDATE paths). The machinery behind it is real: a related fetch that would block the serial contract loop is deferred to an off-loop waiter, bounded by MAX_INFLIGHT_DEFERRALS = 256 with an RAII guard giving exactly-once resume, and an over-cap op surfaces MissingRelated rather than growing unboundedly (freenet-core#4391, crates/core/src/contract.rs). freenet-core#2870 ("Complete related contract mechanism implementation") is still open but is itself partly stale — the UPDATE-path todo!() it cites at runtime.rs:946 no longer exists.

The thing to get right is not whether it works, but what you are allowed to read. A contract's verdict must be a function of its inputs, or replicas diverge. Reading another contract widens the input set to something that changes underneath you:

• Reading an immutable fact (a certificate, a signed key) is safe — every peer gets the same answer forever.
• Reading a monotonic fact in the once-true-always-true direction is safe.
• Gating validity on mutable or growing state is not. "Reject if the other party has more than N entries" flips from valid to invalid as their state grows, so peers validating at different moments disagree and never converge. That class of rule belongs in client-side policy, not in validate_state.

Practical limits:

• One round only. A RequestRelated is fetched and retried exactly once; a second is an error (contract/executor/runtime/contract_ops.rs:431-432), capped at MAX_RELATED_CONTRACTS_PER_REQUEST = 10 ids. No chained dependencies.
• On the client-facing UPDATE surface, UpdateData::RelatedStateAndDelta is the form you send; bare UpdateData::RelatedState / RelatedDelta are rejected from ContractRequest::Update and reserved for the runtime's own request-related orchestration, which surfaces RelatedState to your WASM itself.
• A related fetch that times out can wedge an UPDATE merge (freenet-core#4077, open).
• Related state resolved during validation is captured, since v0.2.131 (2026-08-24) — freenet-core#5393 and #5402. Before that, a contract whose validity depended on another contract was permanently unjudgeable, and an unjudgeable contract reads exactly like a clean one. Note issue #5376 closed on 2026-09-06, a fortnight after the code shipped: a close date is bookkeeping; the release tag is what makes a mechanism available. Checking that for yourself has its own trap — this repo squash-merges, so the SHAs an issue timeline cites are branch commits that never exist in main. Searching the log for them, or for the issue number, finds nothing in any tag and reads exactly like "never shipped". Go by PR number, and confirm with merge-base --is-ancestor <merge-sha> <tag>.
• Judgeable is not judged. The verifier never fetches related state; it replays only what the bundle already carries, mapping any RequestRelated straight to Inconclusive::RelatedRequired (conformance/verifier.rs:997-1005). Production is stricter — the executor fetches and re-validates once at depth=1 (executor_impl.rs:2461) — and that path is never exercised by the verifier. Capture also keeps only the most-recently-observed state per related contract, so a defect needing a specific or older one yields no verdict at all: measured 1,567 of 5,856 replayed cases inconclusive for want of related state, five contracts with no verdict on any case (conformance/capture.rs:108-125). That file states the intent plainly — "depending on related state must not be a way to escape conformance checking" — and coverage starvation is how it still can.
• fdev verify-merge --state <files> is blind to related contracts. The non---bundle path leaves related unconditionally empty (fdev/src/conformance.rs:912-915), so a contract of this shape comes back 100% inconclusive on every property — which, skimmed for violations, reads as a clean bill. Check on the --bundle path, confirm the bundle reports related_entries > 0, count the explicit verdicts, and treat inconclusive as not a pass. Exit code 4 means violations were found and the JSON is complete.
• freenet-scaffold's #[composable] has no inter-contract awareness (freenet-core#2870), so cross-contract dependencies are hand-rolled.

The mechanism with code, and which of the two paths to request related state from, is in references/state-authorization-patterns.md → "Related-Contracts Mechanism".

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Development Workflow

Follow these phases in order.

Building on an app you do NOT own — reading River rooms, using the ghostkeys delegate, indexing another project's contracts? Do not hardcode their contract or delegate key. It is BLAKE3(BLAKE3(wasm) ‖ params), so it moves on every re-key of theirs, including a bare version bump, and the failure is silent: every read comes back looking like "this user has nothing stored". Pinning a version of their crate does not help — that pins you to their view of the key as of their release, which is the thing that went stale. Fetch their key at runtime instead: resolve their author-signed pointer if they publish one, and otherwise read it from their webapp bundle, which is what ghostkeys does today. Pointer adoption is thin, so expect the fallback to be the path for most apps right now. Either beats a compiled-in constant. See references/building-on-other-apps.md.

Working on an app that already exists? Before anything else, check whether it hardcodes a delegate key belonging to a platform delegate it does not own (ghostkeys being the one in use today). That constant goes stale on every re-key of that delegate — including a bare version bump — and the failure is silent: every request comes back looking like "this user has nothing stored". One grep, and the fix is a runtime fetch. See references/delegate-patterns.md → "Depending on Someone Else's Delegate". This broke every ghostkeys integration in August 2026 and was found by a confused user rather than by any test.

Already shipped v1 and here to UPGRADE? (bump freenet-stdlib, ship a new contract/delegate version, or fix a bug that re-keys the WASM) — go straight to references/upgrade-and-migration.md → "Upgrading a Freenet dApp — the painless path", the single start-to-finish playbook. A routine WASM/stdlib bump is low-risk and mechanical when you designed for it at v1, not "recreate everything and all invites die" — River's live 0.6→0.8 stdlib re-key (verified 2026-07-12) auto-migrated every room on refresh, kept every invite and the 78-member Official room intact, and needed no recreation. The phases below build a new dApp; the playbook ties the upgrade steps together (v1 design precondition → reproducible builds → register the outgoing hash → freenet-migrate → publish → do NOT recreate instances or warn of dead invites).

Phase 1: Contract Design (Shared State)

Start by listing each kind of shared state your app needs — each kind becomes its own contract crate. Then design each one in turn using the questions below.

Key questions (per contract):

• What data must all users see consistently for this concern?
• How should conflicts be resolved when two users update simultaneously?
• What cryptographic verification is needed?
• What are the state components and their relationships?
• What parameters distinguish one instance from another (e.g. room owner key, profile owner key)?
• If users reference each other (messaging, contacts, profiles), what is the user-facing identifier? It should be short, self-certifying, and stable across WASM upgrades — derived from a key, never a contract key. See identity-and-addressing.md.
• How is each record inside this state identified, and does that id cover every term a reader will later rely on it to bind? A writer-supplied nonce, or an id that hashes only some of a record's terms, lets one author sign two different records under one id — and under a first-writer-wins merge that is permanent divergence that cannot heal, because both peers' summaries already name the id. Derive ids from content, compute them in the contract, and have exactly one function decide "are these the same thing". Get this right before launch: changing a derivation afterwards makes every published record unverifiable, which is a breaking change to users' data. See contract-patterns.md → "Record Identity".
• Can strangers write to this contract? If so, what stops one attacker minting ten thousand keys and flooding it? There is no server to host a CAPTCHA, so the mechanisms available are proof-of-work and ghost keys (a blind-signed certificate proving an anonymous donation — a cost the attacker cannot beat with better hardware, and not burned as waste heat). The recommended shape is both: proof-of-work as the always-sufficient default, with a ghost key offered as a way to skip the wait, surfaced while the grind is running and the user is blocked anyway. That lets you set difficulty by what deters an attacker rather than by what your slowest device tolerates, while never pricing anyone out. See identity-and-addressing.md → "Cryptographic CAPTCHA". Present the choice to the developer rather than picking silently: ghost keys cost their users money, that money funds Freenet, and the mint is centralized (verification is not). Those are product and architecture decisions, not technical details to settle on the developer's behalf.
• How large can this contract's state realistically grow? Keep each contract instance's state small — target well under 4 MB, not just under the host's 50 MiB hard cap. A GET transfers the entire state before the UI can render anything, so state size is felt directly as load latency, and validate_state/update_state/summarize_state WASM execution cost scales with it too. If a kind of data can grow without bound (message history, uploaded files, a membership list that only grows), don't let one contract instance absorb all of it — shard by the natural unit of write concurrency instead (one contract per room, per user, per time-window, per shard-key, etc.), so each instance stays small regardless of how large the dataset gets in aggregate. See state-authorization-patterns.md → "State Size Budget".

Implementation steps:

1. Define state structure using #[composable] macro from freenet-scaffold
2. Implement ComposableState trait for each component
3. Implement ContractInterface trait for the contract
4. Ensure all state updates satisfy the merge laws (associative, commutative, idempotent), and that get_state_delta returns a negligible delta (ideally zero bytes, never state-sized) when the requester's summary already matches your state (see contract-patterns.md)
5. Every field in state must be covered by a cryptographic signature -- contracts run on untrusted peers who can modify unsigned fields. Write a test for each signed field verifying that tampering causes verification failure. See contract-patterns.md for versioned signature patterns when adding fields later.
6. Plan contract upgrade from v1 — it's low-risk and mechanical when you design for it. The property that makes it mechanical is that a new contract version accepts old contract state, so migration is pure data transfer and any client can carry a user forward — including a user who never opens your app again. Once you have users that stops being a preference and becomes a constraint on which changes you may make: a change to how a record's identity is derived breaks it by construction, and is a breaking change to users' data rather than an internal refactor. See upgrade-and-migration.md → "A New Version Must Accept Old State". A WASM change moves the contract key, but if you anchor your app's durable references on a stable identity anchor independent of the WASM — an owner/user key, fixed singleton params, a DID, or an index contract mapping a stable name → current key (options in upgrade-and-migration.md step 1) — the upgrade is transparent: the client re-derives the new contract key from the unchanged anchor, so invites, share links and membership survive. River's 0.6→0.8 re-key on the live network kept every room and invite; recreation is only for deliberately rotating the anchor itself, never for a routine contract/stdlib bump. State is carried forward by a backward probe from a committed legacy-code-hash registry, packaged by the freenet-migrate crate (0.6.0, with freenet-migrate-build 0.2.0) — do not hand-roll it. Read the freenet-app-migration skill before writing any of it, if you have it: it owns the migration doctrine — when to probe, which probe outcomes may seal a completion marker, and the failure modes that lose data with a green build. It ships separately from this plugin, so if it is not installed, contract-patterns.md and upgrade-and-migration.md carry the same rules and are enough to build against. See contract-patterns.md → "Contract WASM Upgrade & State Migration" for the key-derivation mechanism, upgrade-and-migration.md for the operational discipline, and the freenet-migrate-adoption skill for swapping an existing hand-rolled sweep over to the crate.
7. Read state-authorization-patterns.md before designing the second iteration. It captures cross-cutting patterns (per-item vs bundled signatures, replay protection via monotonic counter / tombstones / cross-context binding, signed-payload hygiene, why a contract must not read the host clock and what to carry instead, related-contracts limits, wire-format stability) that bite on every contract beyond the trivial.

References:

• references/contract-patterns.md — ContractInterface, the merge laws, composable state, basic signatures.
• references/state-authorization-patterns.md — authentication, replay protection, signed-payload hygiene, time (contracts must not read the host clock), related-contracts, wire-format stability, common pitfalls.
• references/identity-and-addressing.md — short self-certifying user-facing addresses, keeping large (post-quantum) keys out of identifiers, identity that survives WASM upgrades, and blocking bots without a server (ghost keys vs proof-of-work).

Phase 2: Delegate Design (Private State)

Determine what private data each user needs stored locally and split it across delegates by responsibility (e.g. one delegate per trust boundary or per long-running background task). Most apps need at least one delegate; many need several.

Know the limits before you lean on a delegate for background work. A delegate runs only when something pokes it: there is no scheduled wakeup (freenet-core#3972), and freenet-stdlib 0.11.0 removed the DelegateCtx::schedule_wakeup wrapper that no node ever implemented. Contract GET and SUBSCRIBE do reach the network now (freenet-core#5615), but a subscription is not re-registered after the node restarts, so it does not keep a contract alive across one (freenet-core#4669, open). Contract access is by message only. ctx.put_contract_state, ctx.update_contract_state and ctx.subscribe_contract are gone — emit PutContractRequest / UpdateContractRequest / SubscribeContractRequest instead. On stdlib 0.10.0 and earlier those wrappers still compile and then fail at module instantiation, which is why 0.11.0 removed them. Test that work against a real node: freenet local never runs the loop that services a delegate's contract requests, so a delegate's GET, PUT, UPDATE and SUBSCRIBE all silently do nothing there (freenet-core#5273). references/delegate-patterns.md → "Delegate Capabilities" has the verified detail and the current state.

Key questions (per delegate):

• What user-specific data needs persistence? (keys, preferences, cached data)
• What signing/encryption operations are needed?
• What permissions are needed for sensitive operations?
• Does a platform delegate already do this? Delegates are callable across apps, so some responsibilities are worth borrowing rather than building. ghostkeys is the one that exists today: it holds the user's ghost-key identities and signs on your behalf, and it renders the user's allow/deny prompt itself, so you implement no permission flow. See identity-and-addressing.md → "Cryptographic CAPTCHA" for what it is for, how it pairs with proof-of-work as an escape hatch rather than replacing it, and the two caveats worth relaying to the developer: the mint is centralized, and Freenet has a funding interest in you choosing it.

Implementation steps:

1. Define request/response message types
2. Implement DelegateInterface trait
3. Handle secret storage operations (Store, Get, Delete, List)
4. Implement cryptographic operations (signing, encryption)
5. Design for secret migration from v1 -- when delegate WASM changes, the delegate key changes and all stored secrets become inaccessible. There is no ExportSecrets request in the stdlib wire protocol and no node-level copy-forward. The mechanism messages each old delegate key via DelegateRequest::ApplicationMessages, re-running the old WASM to read its secrets, and folds the signing keys forward (encryption secrets are re-derived) — so only a predecessor whose already-deployed WASM answers can be recovered from, which makes this forward-only. freenet-migrate ships that answer as handle_export_request (since 0.3.0) for you to call from your delegate; River needs no special handler only because its chat delegate already answered a general-purpose GetRequest/ListRequest over its own secret namespace, which most delegates do not. Every release shipped without an export answer adds one permanently unrecoverable generation — see delegate-patterns.md → "A delegate migration is forward-only". Keep a committed registry of old delegate keys and migrate promptly — the re-run breaks after a stdlib/ABI bump (freenet/river#204). See delegate-patterns.md for the mechanism; freenet-migrate codifies the delegate registry and build codegen, but delegate secret carry-forward has no core mechanism and never will — a node-level attempt (RegisterDelegateWithPredecessors) was built, shipped, then found forgeable and disabled as a security fix (freenet-core#5199), and after three rejected trust-model designs, app-level migration is settled standing policy, not an interim measure. App-level does not mean bespoke: freenet-migrate ships the delegate-side entry points (migrate_delegate_secrets, register_delegate_with_migration, unchanged since 0.5.0; crates.io is now 0.6.0, whose break is contract-half only), and River, Delta and ghostkeys all drive them on main at 0.5.0. Note that River and Delta run the crate's walk alongside their existing hand-rolled sweep, which stays authoritative for now; retiring the sweep is a later release, after the walk field-validates. See delegate-patterns.md → "Delegate secret migration: no core mechanism, and why" for the full history, the freenet-migrate-adoption skill for the swap procedure, and freenet-core#2776 for live status. See upgrade-and-migration.md for the operational discipline (resumable/interrupted-migration recovery, migration telemetry, and the upgrade test harness).

Reference: references/delegate-patterns.md

Phase 3: UI Design

Build the user interface connecting to contracts and delegates. Two approaches:

Option A: Dioxus (Rust → WASM)

Best for: teams already in Rust, complex state logic shared with contracts.

Implementation steps:

1. Set up Dioxus project with WASM target
2. Implement WebSocket connection to Freenet gateway
3. Create synchronizer for contract state subscriptions
4. Implement delegate communication for private storage
5. Build reactive UI components
6. Vendor your stylesheets, fonts, and scripts. The gateway serves every webapp under a same-origin CSP — CDN <link> / <script> tags from cdn.jsdelivr.net, cdnjs.cloudflare.com, fonts.googleapis.com, etc. are blocked in production even though they work in dx serve / vite dev. See references/ui-patterns.md "Gateway CSP: Vendor Your Assets".

Option B: TypeScript + Vite

Best for: web developers, faster iteration, familiar tooling (npm, SCSS, etc.).

Implementation steps:

1. Set up Vite project with @freenetorg/freenet-stdlib (TypeScript package)
2. Use FreenetWsApi class for WebSocket connection (handles FlatBuffers serialization)
3. Pass empty string auth token to FreenetWsApi constructor (sandbox blocks cookie reading)
4. Use Vite define to inject contract hashes and delegate key bytes at build time
5. For delegate communication, dynamically import internal FlatBuffers types (ClientRequestT, ApplicationMessagesT, etc.)
6. Build reactive UI with vanilla TS, or any framework (React, Vue, Svelte)

Validate the UI in a real browser (both options)

A Freenet UI's real render path only runs in a browser. A Dioxus UI ships as a WASM bundle, so rendering a component tree to a string in a Rust test does not exercise the compiled bundle, its event handlers, or its asset paths, and both options reach the node over a WebSocket that unit tests never touch. Drive the UI with Playwright (or equivalent browser automation) from the first screen onward, not only at release time. Treat "I built the component" as unfinished until a browser has loaded it and a script has clicked through it.

1. Serve the UI locally (dx serve for Dioxus, vite dev for TypeScript) and drive it with Playwright against mock or offline data, so render correctness, navigation, and form validation gate every PR. This is the offline tier in references/production-smoke-testing.md, which has a starter spec.
2. Assert the browser console is clean in every flow. WASM panics, failed requests, and CSP blocks surface only as console or network errors, so a UI that looks correct in a screenshot can still be panicking on every interaction.
3. Once a local node is running, re-run the same flows against the gateway-served webapp (the iso tier). Reaching your app there needs frameLocator and an absolute-URL goto, because the gateway wraps every webapp in an iframe shell.

For interactive debugging rather than scripted specs, the Playwright MCP browser tools drive a running dx serve or local node directly. See the local-dev skill, "Debugging with Playwright".

Tell users who made it and where the source is (both options)

Strongly recommend that every dApp shows a way to reach its author and to find its source code. Raise this with the developer before the first publish if they haven't planned for it. Many sites on Freenet today give no way to contact the person who made them. Nobody can report a bug, ask a question, or offer a fix, and nobody can audit what the app does with their data. On a network whose pitch is "you don't have to trust a server", source that can't be found is a real cost.

Any one of these is enough, and more than one is better:

• Source repository: a GitHub/Codeberg/etc. URL, or a repository hosted on Freenet itself. If the app is open source, link the exact repo the published WASM was built from.
• Email address: a dedicated or pseudonymous address is fine.
• River member ID: so users can find the author in a River room (the Freenet Official room is the obvious one) and message them directly. Also give the full verifying key (River's member info panel shows it). The short member ID is a 40-bit truncation that two members can share, so on its own it can be impersonated.

A pseudonymous channel counts. The aim is to give users a channel to the author, not to reveal who the author is, so an author who wants anonymity can still do this.

Put it where a user will find it without hunting, such as a footer or an "About" page, and ship it in the first release. Many people will only ever see that version. Make each web link a plain <a href>, which the gateway opens in a new tab (target="_blank" rel="noopener" is fine too). Do not navigate by assigning window.location: the shell's frame-src 'self' blocks it and the click silently does nothing.

References:

• references/ui-patterns.md - WebSocket connection models, gateway CSP, serving large binary assets from a dedicated contract, framework-specific patterns.
• references/production-smoke-testing.md - the four test tiers, the development-loop browser-validation recipe, and the iframe-shell Playwright idioms.

Phase 4: Build, Test, and Deploy

Set up the build system, CI, and deployment pipeline.

Implementation steps:

1. Set up build orchestration — either Makefile.toml (cargo-make) or plain Makefile

2. Add a preflight task that runs fmt, clippy, tests, and migration checks before publish

3. Add GitHub Actions CI workflow (runs on push and PRs)

4. Back up contract state to the delegate for network resilience

5. Add a production-liveness smoke test. A ~50-line Playwright spec asserting the gateway-hosted webapp mounts, vendored CSS loaded, and the browser console is clean catches CSP blocks, iframe-shell mistakes, and broken archives that no unit test reaches. See references/production-smoke-testing.md.

6. Check the gateway port, and make the build reproducible. The gateway runs on 7509 — older docs and scripts still reference 50509. For byte-reproducible webapp archives across build hosts, invoke tar with the GNU flags listed under "Tooling Preflight" in references/build-system.md.

   Contracts need more than reproducible tars, and this part is not optional — the WASM bytes are the contract's address. Build them through one canonical script that remaps CARGO_HOME, RUSTUP_HOME and the repo root, and that refuses the build if any build-machine path survives into the WASM. Remapping only your own source path leaves the cargo registry's absolute paths in the bytes, which binds every contract to the machine that built it. Have the script take its target dir as an argument, so any build whose hash you record or pin can go into a throwaway one. See "Byte-reproducibility" in references/build-system.md.

7. Publish the UI as a web container contract — its URL is permanent, and you upgrade in place. Shipping a new release does not rotate the gateway URL: the UI is the container's state, while the contract key is BLAKE3(BLAKE3(container_wasm) || publisher_key) and neither input contains your UI. fdev website init once (it prints your URL and writes your signing key), then fdev website publish / fdev website update for every release thereafter. Back up the signing key on day one — lose it and the site is frozen at its last version forever, and no redirect can rescue it. Keep fdev's built-in versioning unless you have a concrete reason not to: a hand-rolled counter seeded below the stored version bricks the site permanently, so if you must switch, seed strictly above the current on-network version. Whether to pin the container WASM with --contract-wasm is a real trade-off (stable address vs. freezing a third-party contract implementation) — read it before deciding. See references/web-container-contract.md. Do not build a redirect/pointer contract for stable URLs; you already have one.

   Before the first fdev website publish, check that the UI shows a way to contact the author and find the source (see Phase 3, "Tell users who made it"). If it doesn't, stop and ask the developer.

8. Plan contract-WASM stability before the first release. A cargo update in the workspace root must not silently rotate contract IDs. See references/build-system.md → "Per-contract lockfile isolation".

9. Test the upgrade path and make migration resumable. The dangerous inputs are old-state -> new-code and interrupted migration, neither exercised by testing the new version on fresh state. Add an old-format-load test and an interrupted-migration-recovery test, and make migration idempotent + resumable (in-progress marker cleared only on full success) + non-destructive + regression-gated + observable. See references/upgrade-and-migration.md.

References:

• references/build-system.md — build, CI, packaging, tooling preflight, per-contract lockfile isolation, contract-ID reproducibility caveat, pre-commit hook for stray .wasm.
• references/production-smoke-testing.md — iframe shell architecture, Playwright recipe for post-publish liveness checks.
• references/web-container-contract.md — how a webapp is addressed and upgraded in place at a permanent URL, fdev website, version monotonicity, key backup, and the size budget.
• references/facade-pattern.md — indirection for the rare case where you must move an audience to a different contract (container-WASM migration or publisher-key rotation). Not needed for ordinary releases.
• references/upgrade-and-migration.md — operational discipline for safe contract/delegate upgrades: the five migration properties (idempotent, resumable, non-destructive, regression-gated, observable), enumerating dynamic key families, the upgrade test harness, and staged reversible rollout.
• references/building-on-other-apps.md — the consumer side: integrating with a contract or delegate you do not own, resolving the author's pointer instead of pinning a key, the seven outcome arms, and what a pointer does not tell you.

Project Structure Templates

Dioxus (Rust) UI

my-dapp/
├── common/                    # Shared types between contract/delegate/UI
│   └── src/
│       ├── lib.rs
│       └── state/            # State definitions
├── contracts/                 # one subdirectory per contract crate
│   ├── room-contract/
│   │   ├── Cargo.toml
│   │   └── src/lib.rs        # ContractInterface implementation
│   └── profile-contract/      # add more as the app grows
│       └── ...
├── delegates/                 # one subdirectory per delegate crate
│   ├── chat-delegate/
│   │   ├── Cargo.toml
│   │   └── src/lib.rs        # DelegateInterface implementation
│   └── identity-delegate/     # add more as the app grows
│       └── ...
├── ui/
│   ├── Cargo.toml
│   ├── Dioxus.toml
│   └── src/
│       ├── main.rs
│       └── components/
├── Cargo.toml                # Workspace root
└── Makefile.toml             # cargo-make build tasks

TypeScript + Vite UI

my-dapp/
├── contracts/
│   └── my-contract/
│       ├── Cargo.toml
│       └── src/lib.rs        # ContractInterface implementation
├── delegates/
│   └── my-delegate/
│       ├── Cargo.toml
│       └── src/lib.rs        # DelegateInterface implementation
├── web/
│   ├── package.json
│   ├── vite.config.ts         # Injects contract/delegate keys at build time
│   ├── tsconfig.json
│   ├── index.html
│   └── src/
│       ├── index.ts           # Entry point, connection flow
│       ├── freenet-api.ts     # FreenetWsApi wrapper
│       ├── delegate-api.ts    # Delegate FlatBuffers message building
│       ├── identity.ts        # Identity management (delegate + fallback)
│       ├── types.ts           # Shared TypeScript types
│       └── components/        # UI components
├── Cargo.toml                 # Workspace root (contracts + delegates)
└── Makefile                   # Build orchestration

Reference Project

River demonstrates all patterns:

• Contracts: contracts/room-contract/
• Delegates: delegates/chat-delegate/
• UI: ui/
• Common types: common/

Key Dependencies

Track the versions River (the reference dApp) uses. Mismatched versions cause deserialization failures, missing features, and "variant index out of range" errors. Check River's workspace Cargo.toml before pinning.

As of September 2026 — River pins freenet-stdlib = "0.8.5". That is no longer the latest crates.io release: 0.9.0 and 0.10.0 followed, and 0.11.0 is the one a DELEGATE crate wants, because it removes the DelegateCtx write and subscribe methods that 0.8.5 through 0.10.0 expose and no node implements — calling one compiles, publishes, and then fails at module instantiation (see references/delegate-patterns.md). For contract and UI crates, River's pin is still the version to mirror. If you are moving code off an older pin, the step is 0.6 → 0.8 (no 0.7 was ever published to crates.io): it added Base58-stringified contract_states keys in NodeDiagnosticsResponse, hardened wire-boundary enums with #[non_exhaustive], and removed the world-known DEFAULT_CIPHER / DEFAULT_NONCE constants, so you need the wildcard match arms / random cipher generation documented in references/delegate-patterns.md.

DEFAULT_CIPHER/DEFAULT_NONCE is the break that gets quoted, but it is not the only one. ContractInstanceId::from_bytes is deprecated as of 0.8.5 in favour of from_base58 — it is a delegating alias, so it still compiles, but a crate built with -D warnings (most CI) fails on it. Check the version before acting on this: from_base58 does not exist in 0.8.2, 0.8.3 or 0.8.4, so a port that stops short of 0.8.5 sees no warning and has nothing to change. Note what the rename is telling you: it parses base58 text, not raw bytes. If you were passing it a raw 32-byte id it was already wrong; the replacement there is ContractInstanceId::new([u8; 32]), not from_base58. Budget a compile-and-read pass over the deprecation warnings rather than assuming a single documented break is the whole list.

# Workspace-wide (Cargo.toml) — matches River pin.
freenet-stdlib = { version = "0.8.5", features = ["contract"] }
freenet-scaffold = "0.2.2"
freenet-scaffold-macro = "0.2.2"

# UI crate (ui/Cargo.toml): enables WebApi/WebSocket helpers
freenet-stdlib = { workspace = true, features = ["net"] }

# UI framework
dioxus = { version = "0.7.9", features = ["web"] }

The contract feature is required for contract crates targeting wasm32-unknown-unknown; use the delegate feature for delegate crates. The net feature pulls in WebApi for the UI.

TypeScript UI

For UIs built with TypeScript + Vite (Option B in Phase 3), depend on the matching @freenetorg/freenet-stdlib release:

{
  "dependencies": {
    "@freenetorg/freenet-stdlib": "^0.2.0"
  },
  "devDependencies": {
    "vite": "^6.0",
    "typescript": "^5.0",
    "sass": "^1.0"
  }
}

The TS package v0.2.0 brought the API to parity with the Rust client: FreenetWsApi with promise-based get/put/update (await api.X(...), resolves/rejects on the matching response), full ResponseHandler including onContractNotFound/onSubscribeResponse/ onClose, inbound ReassemblyBuffer, and transparent outbound chunking for payloads >512 KB. Callbacks still fire alongside the promise-based calls for backward compatibility; the default request timeout is 30 s. subscribe is also promise-based from TS package 0.4.0 (resolves/ rejects on the matching SubscribeResponse); on the npm-published 0.3.0 and earlier it resolves as soon as the request is sent, never on the host's response — use the ResponseHandler callbacks to detect a refused subscribe on those versions. disconnect resolves on send in every version. See references/ui-patterns.md for the full pattern (including which stdlib version you need for which behavior) and a warning about the private sendRequest cast used for delegate messages until a public builder lands.

Security: removed encryption defaults

stdlib v0.8.0 (PR #75) removed the public constants DEFAULT_CIPHER and DEFAULT_NONCE to close a CVE-class issue (world-known keys leaked into any binary that imported them). They are still present in 0.6.0 and 0.6.1. Delegates that previously used these must now generate random values per session — e.g. let key: [u8; 32] = rand::random(); let nonce: [u8; 24] = rand::random();. Code still referencing the old constants will fail to compile against stdlib 0.8 or newer.

It is not the only break on the way to current stdlib, and treating it as the whole list is how a -D warnings build fails after the port looks finished — see "Key Dependencies" above for ContractInstanceId::from_bytes → from_base58 (0.8.5).

---

Improving This Skill

This skill is designed to be self-improving. When encountering issues while using this skill, agents should file GitHub issues or submit PRs to improve it.

When to File an Issue

File an issue at freenet/freenet-agent-skills when:

• Instructions are unclear or ambiguous
• Information is missing for a common use case
• Code examples don't compile or are outdated
• Patterns don't match current River implementation
• A referenced API has changed

How to File an Issue

gh issue create --repo freenet/freenet-agent-skills \
  --title "dapp-builder: <brief description>" \
  --body "## Problem
<describe what was unclear or incorrect>

## Context
<what were you trying to accomplish>

## Suggested Improvement
<optional: how the skill could be improved>"

Submitting a PR

For concrete improvements:

# Clone and create branch
gh repo clone freenet/freenet-agent-skills
cd freenet-agent-skills
git checkout -b improve-<topic>

# Make changes to dapp-builder/SKILL.md or references/*.md
# ... edit files ...

# Submit PR
git add -A && git commit -m "dapp-builder: <description>"
gh pr create --title "dapp-builder: <description>" \
  --body "## Changes
<describe improvements>

## Reason
<why this helps>"

What Makes a Good Improvement

• Fixes factual errors or outdated information
• Adds missing patterns discovered while building a dApp
• Clarifies confusing instructions based on real usage
• Adds test examples that would have helped
• Updates code to match current Freenet/River APIs