Elasticsearch ES|QL

Generate ES|QL queries from natural language descriptions and execute them against Elasticsearch.

For visualization tasks: Always read references/vega-lite-reference.md first. It contains the complete grammar of graphics including data types, encoding channels, mark types, multi-view composition (layer, facet, concat, repeat), and professional best practices.

For architecture diagrams: Use the graphviz_chart tool with DOT syntax. Best for flowcharts, dependency graphs, state machines, and system architecture diagrams. Always read references/graphviz-reference.md for complete syntax, node shapes, edge styles, and layout patterns.

What is ES|QL?

ES|QL (Elasticsearch Query Language) is a piped query language for Elasticsearch. It is NOT the same as:

• Elasticsearch Query DSL (JSON-based)
• SQL
• EQL (Event Query Language)

ES|QL uses pipes (|) to chain commands: FROM index | WHERE condition | STATS aggregation BY field | SORT field | LIMIT n

Version Compatibility: ES|QL was introduced in 8.11 (tech preview) and became GA in 8.14. Features like LOOKUP JOIN, MATCH, and INLINESTATS were added in later versions. Check references/esql-version-history.md for feature availability by version.

Container Environment

Inside Docker containers, the skill is available at:

ESQL="{baseDir}/esql.js"

Environment Configuration

Elasticsearch connection is configured via environment variables (set by the container):

# Option 1: Elastic Cloud (recommended)
export ELASTICSEARCH_CLOUD_ID="deployment-name:base64encodedcloudid"
export ELASTICSEARCH_API_KEY="base64encodedapikey"

# Option 2: Direct URL with API Key
export ELASTICSEARCH_URL="https://elasticsearch:9200"
export ELASTICSEARCH_API_KEY="base64encodedapikey"

# Option 3: Basic Auth
export ELASTICSEARCH_URL="https://elasticsearch:9200"
export ELASTICSEARCH_USERNAME="elastic"
export ELASTICSEARCH_PASSWORD="changeme"

# Optional: Skip TLS verification (development only)
export ELASTICSEARCH_INSECURE="true"

Usage

Generate Query Only (for review)

$ESQL generate "show me the top 10 errors from logs in the last 24 hours"

Get Index Information (for schema discovery)

$ESQL indices                    # List all indices
$ESQL indices "logs-*"           # List matching indices
$ESQL schema "logs-2024.01.01"   # Get field mappings for an index

Execute Raw ES|QL

$ESQL raw "FROM logs-* | STATS count = COUNT(*) BY host.name | SORT count DESC | LIMIT 5"

Execute with TSV Output (for charting)

$ESQL raw "FROM logs-* | STATS count = COUNT(*) BY component | SORT count DESC" --tsv

TSV Output Options:

• --tsv or -t: Output as tab-separated values (clean, no decorations)
• --no-header: Omit the header row

Test Connection

$ESQL test

Visualization with vega_chart Tool

The vega_chart extension renders Vega-Lite specifications as PNG images directly in your terminal. This gives you full control over visualization design using the declarative grammar of graphics.

Important: Before creating any charts, read the complete Vega-Lite Reference for data types, encoding channels, mark types, multi-view composition patterns, and best practices.

Why Vega-Lite?

Rather than rigid chart types, Vega-Lite provides a grammar of graphics:

• Declarative: Describe what you want, not how to draw it
• Composable: Layer, facet, concatenate, and repeat views
• Professional: Control over every visual detail

Basic Workflow

1. Get TSV data from esql.js using --tsv flag
2. Transform field names - rename dot-notation fields to simple names (see Critical Pitfalls)
3. Construct a Vega-Lite spec (JSON) with inline data
4. Call vega_chart tool with the spec

Critical Pitfalls

⚠️ These issues WILL break your charts. Read carefully.

1. Dot-Notation Field Names Break Everything

Problem: ES|QL returns fields like room.name, host.ip, metric.value. Vega-Lite interprets dots as nested object paths, looking for {room: {name: value}} instead of {"room.name": value}.

Symptom: Axis labels show "undefined", bars collapse into single row, legends show "undefined".

Solution: Always use inline data with renamed fields:

// ❌ WRONG - will show "undefined"
{
  "data": {"values": [{"room.name": "Kitchen", "temp": 21}]},
  "encoding": {"y": {"field": "room.name"}}
}

// ✅ CORRECT - use simple field names
{
  "data": {"values": [{"room": "Kitchen", "temp": 21}]},
  "encoding": {"y": {"field": "room"}}
}

Workflow: Query ES|QL → Copy values → Create inline data with renamed fields.

2. TSV Data with Complex Fields

When using tsv_data parameter, field names with dots will fail. Always use inline data.values instead and manually construct the data array with clean field names.

3. Horizontal Bar Chart Labels Get Truncated

Problem: Y-axis labels on horizontal bar charts get cut off by default.

Solution: Add labelLimit to axis config:

"encoding": {
  "y": {
    "field": "category",
    "axis": {"labelLimit": 200}
  }
}

4. Facet/Repeat Syntax Incompatible with Altair v6

Problem: Top-level facet and repeat with spec don't work in the vega_chart renderer (uses Altair v6).

Solution: Use encoding-based faceting instead:

// ❌ WRONG - facet at top level fails
{
  "facet": {"column": {"field": "region"}},
  "spec": {"mark": "line", ...}
}

// ✅ CORRECT - use column/row in encoding
{
  "mark": "line",
  "encoding": {
    "column": {"field": "region", "type": "nominal"},
    "x": {...},
    "y": {...}
  }
}

Simple Examples

Horizontal Bar Chart (with proper label handling):

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "width": 400,
  "height": 250,
  "data": {
    "values": [
      { "category": "Category A", "value": 28 },
      { "category": "Category B", "value": 55 }
    ]
  },
  "mark": { "type": "bar", "cornerRadiusEnd": 3 },
  "encoding": {
    "y": {
      "field": "category",
      "type": "nominal",
      "sort": "-x",
      "title": null,
      "axis": { "labelLimit": 150 }
    },
    "x": { "field": "value", "type": "quantitative", "title": "Count" }
  }
}

Time Series (with proper aspect ratio):

{
  "width": 600,
  "height": 200,
  "layer": [
    { "mark": { "type": "area", "opacity": 0.3 } },
    { "mark": { "type": "line", "strokeWidth": 2 } },
    { "mark": { "type": "point", "filled": true, "size": 40 } }
  ],
  "encoding": {
    "x": { "field": "date", "type": "temporal", "axis": { "format": "%b %d" } },
    "y": { "field": "value", "type": "quantitative" }
  }
}

Best Practices

1. Always use inline data with simple field names - never rely on TSV with dot-notation
2. Use vertical bar charts when you have many categories - labels display more reliably
3. Time series: 3:1 or 4:1 aspect ratio - wide, not tall
4. Direct labeling over legends - place text labels at line endpoints
5. Never use pie/donut charts - use sorted bar charts instead
6. Color encodes data, not decoration - use single color for single-series data
7. Sort by value ("sort": "-x") not alphabetically

Full Reference (Required Reading)

Always read Vega-Lite Reference before creating visualizations. It contains:

• Data types (N, O, Q, T) and when to use each
• Complete encoding channels (position, color, size, shape, etc.)
• All mark types (bar, line, point, area, rect, boxplot, etc.)
• Scale and axis configuration
• Multi-view composition (layer, hconcat, vconcat) for dashboards
• Professional chart patterns with complete working examples
• Common pitfalls and solutions

Architecture Diagrams with Graphviz

The graphviz_chart extension renders Graphviz DOT specifications as PNG images. Use it for:

• System architecture diagrams
• Data flow diagrams
• Dependency graphs
• State machines
• Flowcharts
• ER diagrams

Important: Before creating diagrams, read the complete Graphviz Reference for DOT syntax, node shapes, edge styles, clusters, and layout engines.

Basic Usage

Call graphviz_chart with a DOT specification:

digraph G {
    rankdir=LR;
    node [shape=box style="rounded,filled" fillcolor=lightblue];

    A [label="Service A"];
    B [label="Service B"];
    C [label="Database" shape=cylinder fillcolor=lightyellow];

    A -> B [label="HTTP"];
    B -> C [label="SQL"];
}

When to Use Graphviz vs Vega-Lite

Use Graphviz	Use Vega-Lite
Architecture diagrams	Data visualizations
Flowcharts	Bar/line/scatter charts
Dependency graphs	Time series
State machines	Aggregations
ER diagrams	Statistical plots
Process flows	Heatmaps

Quick Examples

System Architecture:

digraph architecture {
    rankdir=TB;
    node [shape=box style=filled];

    subgraph cluster_frontend {
        label="Frontend";
        color=lightblue;
        style=filled;
        web [label="Web App"];
    }

    subgraph cluster_backend {
        label="Backend";
        color=lightgreen;
        style=filled;
        api [label="API Server"];
    }

    subgraph cluster_data {
        label="Data Layer";
        color=lightyellow;
        style=filled;
        db [label="PostgreSQL" shape=cylinder];
        cache [label="Redis" shape=cylinder];
    }

    web -> api;
    api -> db;
    api -> cache;
}

State Machine:

digraph states {
    rankdir=LR;
    node [shape=circle];

    start [shape=point width=0.2];
    end [shape=doublecircle];

    start -> idle;
    idle -> running [label="start"];
    running -> paused [label="pause"];
    paused -> running [label="resume"];
    running -> idle [label="stop"];
    running -> end [label="complete"];
}

Key DOT Syntax

• Directed graph: digraph G { A -> B; }
• Undirected graph: graph G { A -- B; }
• Node attributes: A [label="Name" shape=box fillcolor=blue];
• Edge attributes: A -> B [label="calls" style=dashed];
• Clusters: subgraph cluster_name { ... } (must start with "cluster")
• Layout direction: rankdir=LR; (LR, RL, TB, BT)

Layout Engines

Specify with the engine parameter:

• dot (default): Hierarchical, best for DAGs
• neato: Spring model, good for undirected graphs
• fdp: Force-directed, large graphs
• circo: Circular layout
• twopi: Radial layout

Full Reference (Required Reading)

Always read Graphviz Reference before creating diagrams.

Workflow for Query Generation

When asked to generate an ES|QL query:

1. Understand the intent: What data? What operations? What output?

2. Discover schema (if needed):

   $ESQL indices "pattern*"
   $ESQL schema "index-name"
   

3. Read the ES|QL reference for syntax details:

   • ES|QL Complete Reference

4. Generate the query following ES|QL syntax:

   • Start with FROM index-pattern
   • Add WHERE for filtering
   • Use EVAL for computed fields
   • Use STATS ... BY for aggregations
   • Add SORT and LIMIT as needed

5. Execute and visualize:

   $ESQL raw "FROM index | STATS count = COUNT(*) BY field" --tsv
   

ES|QL Quick Reference

Basic Structure

FROM index-pattern
| WHERE condition
| EVAL new_field = expression
| STATS aggregation BY grouping
| SORT field DESC
| LIMIT n

Common Patterns

Filter and limit:

FROM logs-*
| WHERE @timestamp > NOW() - 24 hours AND level == "error"
| SORT @timestamp DESC
| LIMIT 100

Aggregate by time:

FROM metrics-*
| WHERE @timestamp > NOW() - 7 days
| STATS avg_cpu = AVG(cpu.percent) BY bucket = DATE_TRUNC(1 hour, @timestamp)
| SORT bucket DESC

Top N with count:

FROM web-logs
| STATS count = COUNT(*) BY response.status_code
| SORT count DESC
| LIMIT 10

Text search (8.17+):

FROM documents METADATA _score
| WHERE MATCH(content, "search terms")
| SORT _score DESC
| LIMIT 20

Full Reference

For complete ES|QL syntax including all commands, functions, and operators, read:

• ES|QL Complete Reference
• ES|QL Version History - Feature availability by Elasticsearch version
• Query Patterns - Natural language to ES|QL translation
• Generation Tips - Best practices for query generation
• DSL to ES|QL Migration - Convert Query DSL to ES|QL
• Vega-Lite Reference - Complete visualization grammar reference
• Graphviz Reference - DOT language for architecture diagrams

Error Handling

When query execution fails, the script returns:

• The generated ES|QL query
• The error message from Elasticsearch
• Suggestions for common issues

Common issues:

• Field doesn't exist → Check schema with $ESQL schema "index"
• Type mismatch → Use type conversion functions (TO_STRING, TO_INTEGER, etc.)
• Syntax error → Review ES|QL reference for correct syntax
• No results → Check time range and filter conditions

Examples

# Schema discovery
$ESQL test
$ESQL indices "logs-*"
$ESQL schema "logs-2024.01.01"

# Execute queries
$ESQL raw "FROM logs-* | STATS count = COUNT(*) BY host.name | LIMIT 10"
$ESQL raw "FROM metrics-* | STATS avg = AVG(cpu.percent) BY hour = DATE_TRUNC(1h, @timestamp)" --tsv