Tool Overview

This tool checks a Docker Compose YAML file for basic correctness. It parses the YAML, checks that required top-level keys and service fields exist, and runs optional checks for port format, restart policy, and environment variables. It reports syntax and schema errors with line and column when available so you can fix them before running Compose.

Invalid or incomplete compose files cause startup failures and wasted time. Finding missing services or bad structure by hand is slow. This tool runs the checks as you edit and shows where each problem is. A related operation involves validating Dockerfiles as part of a similar workflow.

It is for developers and operators who use Docker Compose. You need basic knowledge of YAML and Compose. No account or sign-in is required. For adjacent tasks, validating Kubernetes YAML addresses a complementary step.

Background and How the Tool Works

Docker Compose uses a YAML file to define services, volumes, and networks. The file must be valid YAML and must have a services section. Each service typically has an image or a build definition. Ports, volumes, and environment variables follow a fixed structure. If the file is invalid YAML or misses required keys, Compose fails. When working with related formats, validating Helm charts can be a useful part of the process.

This tool parses your input as YAML and checks the root structure. It requires that services exist and that each service has a configuration object with either image or build. It checks that ports and volumes, when present, are arrays. It can optionally look for environment variable placeholders and warn about hardcoded passwords or invalid restart policies. It does not run Docker or Compose; it only checks the file in the browser. It does not validate that images exist in registries or that override files merge correctly. In some workflows, validating YAML syntax is a relevant follow-up operation.

People struggle when Compose returns a generic error or when the file is long. The tool reports the first set of problems with line and column when the parser provides them so you know where to look. For related processing needs, validating JSON syntax handles a complementary task.

Key Features

• Single input: One editor for your Docker Compose YAML. You paste or type the file. You can also upload a .yaml or .yml file. The tool validates the content as one YAML document. Input is limited to 500KB and 10,000 lines.
• File upload: You can load a file from disk. Accepted types are .yaml and .yml. The file must be under 500KB. If the content is larger, only the first 500KB is loaded.
• Validate button: You can click Validate to run validation with the current options. When real-time linting is on, validation also runs automatically after you stop typing.
• YAML syntax check: The tool parses the input as YAML. If parsing fails, it reports a syntax error and, when the parser provides it, the line and column of the problem.
• Root and required keys: The root must be a single object. The tool checks that services or version exists at the top level. It requires a services key and checks that it is a mapping of service names to configurations. If version is present, it must be a string or number.
• Service checks: Each service must have a configuration object. Each service must have either image or build. Ports, when present, must be an array; invalid port mapping format is reported as a warning. Volumes, when present, must be an array.
• Optional real-time linting: When the real-time linting option is on, the tool runs extra checks: restart policy must be one of no, always, on-failure, unless-stopped; container_name with multiple services gets a warning; environment entries that look like hardcoded passwords get a warning. You can turn this option off to run only the basic checks.
• Optional environment variable check: When the check environment variables option is on, the tool scans the file for placeholders like ${VAR_NAME} and adds an informational issue listing the variables found and reminding you to define them in .env or the shell. You can turn this option off.
• Result summary: You see either Valid or Invalid and the number of issues. Valid means no errors; warnings and info issues do not make the result invalid.
• Issue list: Each issue has a message, optional line and column, optional suggestion, and a severity: error, warning, or info. Errors block validity; warnings and info do not.
• Sample: A button loads a sample Docker Compose file with version, services, volumes, and networks so you can see a valid structure and try changes.
• Copy: You can copy the editor content to the clipboard.
• Get Fix: When there are issues, you can click Get Fix. The tool sends the YAML and the list of issues to a backend service. You may get plain-text fix suggestions in a modal. You can read or copy them; the tool does not apply them to the editor. This feature may be unavailable or fail.

Common Use Cases

You are writing or editing a docker-compose file and want to catch missing services, invalid YAML, and bad port or volume format before running docker compose up. You paste the file into the tool and fix any reported errors. You use the sample to see a minimal valid compose file. Before committing or deploying, you paste the file here to check syntax and basic structure. When an error is unclear, you use Get Fix to get suggestions if the service is available.

How to Use This Tool

1. Open the tool. You will see an editor on the left and a results area on the right.
2. Paste your Docker Compose YAML into the editor or click Sample to load an example. You can also click Upload and choose a .yaml or .yml file. Keep the content under 500KB and 10,000 lines.
3. Validation runs when real-time linting is on (default) after you stop typing, or when you click Validate. Look at the results area: Valid or Invalid and the number of issues.
4. If there are issues, read each message and the line and column when shown. Fix the YAML in the editor. Common errors: invalid YAML syntax; root not an object; missing services or version; no services defined; services not a mapping; a service missing image or build; ports or volumes not an array. Warnings: invalid port format, invalid restart policy, container_name in multi-service setup, possible hardcoded credentials. Info: detected environment variable placeholders.
5. Use the Options area to turn real-time linting or environment variable checking on or off. Then run Validate again if needed.
6. Use Copy to copy the editor content. Optional: click Get Fix when there are issues to request fix suggestions. Read or copy the suggestions from the modal; the tool does not apply them automatically. Close the modal when done.

What Is Checked and What Is Not

The tool checks YAML syntax, root structure, and the presence of services. It checks that each service has image or build, that ports and volumes are arrays when present, and that port format matches a simple pattern. With options on, it checks restart policy, container_name usage, and possible hardcoded passwords, and it lists environment variable placeholders. It does not run Docker or Compose. It does not validate that images exist in registries, that build contexts exist, or that override files merge correctly. For full behavior use docker compose config or docker compose up in a safe environment.

Reference: Checks Performed

Tips, Limitations and Best Practices

Keep the file under 500KB and 10,000 lines. Use the sample to see a valid structure. Ensure the root is a YAML object with at least services defined. Each service must have image or build. Use environment variables for secrets instead of hardcoded values; the tool can warn when it sees password-like values without placeholders.

The tool does not run Docker or Compose. It does not check that images are available or that build contexts exist. It validates a single file; it does not merge or validate override files. Use docker compose config to validate the full resolved configuration when possible.

Get Fix sends your YAML and the list of issues to a backend service. Do not use it with secrets or sensitive content. If the service fails, use the error messages and line numbers to fix problems by hand.