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Docker Compose Validator

Name: Docker Compose Validator - WebUtil
Author: WebUtil

Validate docker-compose.yml files for correct syntax, structure, and required fields like services, images, and ports.

Docker Compose YAML

Validation Results

What Is a Docker Compose Validator?

A Docker Compose validator checks your docker-compose.yml files for correct syntax, structure, and required fields. Docker Compose defines multi-container applications with services, networks, and volumes. Common mistakes like missing image references, invalid port mappings, or misconfigured environment variables can cause deployment failures. Our Compose file linter helps you catch these issues before running docker compose up.

What We Check in Your Compose File

Services

The top-level services field must exist and contain at least one service definition.

Image / Build

Each service must specify image or build to define how the container is created.

Port Mappings

Port mappings should use the "host:container" format (e.g., "8080:80").

Environment

Environment variables can be a mapping or an array of KEY=VALUE strings.

How to Use This Docker Compose Validator

Paste your docker-compose.yml content into the textarea and click Validate. The tool checks for the version field, verifies that services is defined, validates each service has an image or build, and inspects port mappings, environment variables, and volume/network references. Results show green checkmarks for valid fields and red crosses for issues. Use Load Example for a sample with web and database services. All processing is done client-side.

Tips for Valid Docker Compose Files

Use the correct version — Version 3.8+ is recommended for modern Docker Compose features.
Always quote port mappings — Use "8080:80" (quoted) to prevent YAML parsing issues with colons.
Define networks explicitly — If services communicate, define a custom network at the top level and reference it in each service.
Use .env files for secrets — Reference environment variables via env_file rather than embedding secrets in the Compose file.
Pin image versions — Always specify image tags (e.g., postgres:16-alpine) instead of using latest.

Docker Compose is the standard configuration tool for defining and running multi-container Docker applications locally and in production. Defined in `docker-compose.yml` files, Docker Compose configurations coordinate application services, database containers, volume persistence, internal networks, and environment variables into a single reproducible stack. Because Docker Compose files use YAML, syntax errors like tab characters, incorrect port mapping types (where unquoted `80:80` can be misparsed as base-60 sexagesimal numbers), missing service images or build contexts, and malformed volume mounts can prevent containers from launching or cause subtle networking failures. A Docker Compose validator inspects the structural hierarchy of your compose file, checks service configurations (`services`), verifies network definitions (`networks`), inspects named volumes (`volumes`), and validates port string formats. WebUtil's Docker Compose Validator validates your configuration against modern Compose specifications in real time directly in your browser, keeping your container architecture and environment secrets strictly confidential.

How to Do This in Code

docker compose config --quiet
docker compose config --services
docker compose config --volumes

const yaml = require('js-yaml');
const fs = require('fs');
const doc = yaml.load(fs.readFileSync('docker-compose.yml', 'utf8'));
console.log('Services:', Object.keys(doc.services));

import yaml
with open('docker-compose.yml') as f:
    data = yaml.safe_load(f)
for svc, config in data.get('services', {}).items():
    print(f'{svc}: {config.get("image", "build")}')

import ("os"; "gopkg.in/yaml.v3")

data, _ := os.ReadFile("docker-compose.yml")
var config map[string]any
yaml.Unmarshal(data, &config)

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Related Guides & Tutorials

Web 6 min read

Docker Compose Tutorial for Beginners: Define and Run Multi-Container Apps

Learn Docker Compose from scratch. Define multi-container applications, manage services, networks, and volumes with docker-compose.yml files.

Docker Compose Validator FAQ

What are the essential top-level keys in a docker-compose.yml file?

A modern Docker Compose file requires a services block defining your containers. Optional top-level blocks include networks, volumes, secrets, and configs.

Why does port mapping in Docker Compose sometimes fail or get parsed as octal?

In YAML, unquoted numbers like 80:80 or 22:22 can be interpreted by some YAML parsers as sexagesimal (base-60) numbers. Always quote your port mappings as strings: "8080:80".

What is the difference between Compose File Version 2, 3, and the Compose Specification?

Versions 2 and 3 required a top-level 'version:' attribute. The modern Compose Specification (Docker Compose V2) deprecates the version attribute and provides a unified schema across local dev and cloud deployments.

How should environment variables and secrets be handled in Docker Compose?

Use an .env file for default configuration and Docker Compose 'secrets:' for sensitive credentials rather than hardcoding passwords directly in the YAML file.

Is my compose file or environment configuration uploaded anywhere?

No. WebUtil parses and validates Docker Compose files 100% locally in your browser. Nothing is sent over the network.