Compose static validator

About this tool

Paste a single Compose YAML document and choose Validate YAML to run a bounded, local check. The tool combines a pinned official schema with selected service-reference, dependency and port checks. Each diagnostic includes a line, column and sanitized path. The JSON report excludes source YAML, scalar values and custom names. Editing the input or changing language clears the previous result. Schema acceptance is only one part of the report and never certifies that a deployment will run.

Worked static-validation examples

services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"
    depends_on:
      - cache
  cache:
    image: redis:7-alpine

{
  "schemaValid": true,
  "complete": true,
  "codes": []
}

services:
  web:
    image: nginx:alpine
    ports: "8080:80"

{
  "schemaValid": false,
  "complete": true,
  "codes": [
    "schema"
  ]
}

services:
  web:
    image: nginx:alpine
    depends_on:
      - missing-service

{
  "schemaValid": true,
  "complete": true,
  "codes": [
    "reference"
  ]
}

services:
  web:
    image: "nginx:${TAG}"

{
  "schemaValid": false,
  "complete": false,
  "codes": [
    "interpolation"
  ]
}

Common validation mistakes

• Assuming schema acceptance proves a runnable deployment: review all diagnostics and runtime requirements.
• Writing ports as one scalar instead of a sequence, or misspelling a property: check the schema diagnostic at its line and column.
• Referencing a service or resource absent from this document: fix the declaration or review unresolved include/extends files yourself.
• Expecting ${VARIABLE} or .env to resolve automatically: this tool never reads the host environment or files.
• Sharing the source input instead of the diagnostic report: the textarea still contains original values and may contain credentials.

Limits and notes

• —Input is capped at 100,000 characters, 64 nesting levels, 20,000 parsed/expanded nodes, 1,000 entries per mapping/sequence, 100 aliases and 100 diagnostics. YAML anchors and merge keys are supported within these limits; cyclic aliases, duplicate keys, custom tags, multi-document streams and unsupported non-JSON values are rejected. Reaching a limit leaves validation incomplete.
• —The bundled official Compose Specification schema is pinned to commit 914ec15d1fa498969c0df5c1d672306db3256089, checked on 2026-10-06, using JSON Schema 2020-12. A successful schema check only concerns this snapshot. Your installed Compose implementation or version may not support every field.
• —Variable expressions remain unresolved, including expressions with defaults. The tool never reads host environment variables or .env files. include and extends are not loaded or merged, and external files or URLs are never fetched. These features prevent a complete result; interpolation also prevents schema validity from being established.
• —Semantic checks cover selected declared service/resource references, dependency cycles, static port syntax/ranges and possible host-port overlap. They do not reproduce all Compose rules, profile selection, project merging or runtime scheduling. Unsupported newer semantic areas such as jobs, models and pre-start behavior are reported without execution. Schema-valid can still have semantic errors. No result verifies image availability, build contexts, file existence, credentials, permissions, platform support, live port use or successful deployment. Host-port overlap is a potential conflict, not evidence that a port is occupied.
• —Input is processed in the current browser tab without upload or history storage. The original textarea remains visible. Reports omit source text, scalar values and custom names, but retain known field names, positions and issue types; they are not fully anonymous. Clipboard contents and saved files remain outside the page’s control.

Frequently asked questions

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