YAML Validator

How to Use the YAML Validator

Paste your YAML document into the input field on the left. The tool validates syntax in real time as you type, so you get immediate feedback without pressing any button. If the document contains an error, a clear message appears below the editor showing the exact line and column number where parsing failed, along with a human-readable description of the problem.

Switch between Validate mode and YAML → JSON mode using the toggle at the top of the tool. In Validate mode, a green checkmark confirms the document is syntactically correct. In YAML → JSON mode, the right panel displays the equivalent JSON output, formatted and indented for easy reading. Click Copy to copy the JSON result to your clipboard.

The statistics panel below the editor shows the total key count, maximum nesting depth, and document count, which is useful when auditing large configuration files. Multi-document YAML files (multiple documents separated by ---) are fully supported — each document is parsed independently and results are aggregated. This is particularly helpful when validating Kubernetes manifests that bundle several resource definitions in a single file. No account or installation required; everything runs locally in your browser.

What is YAML Validation?

YAML (YAML Ain't Markup Language) is a human-readable data serialisation format that has become the dominant choice for configuration files in modern infrastructure tooling. Unlike JSON, YAML uses indentation to express structure — there are no curly braces or brackets, making files easier to read and write by hand. However, this reliance on whitespace makes YAML highly sensitive to formatting mistakes that are invisible at a glance.

YAML validation is the process of checking whether a document conforms to the YAML specification before it is consumed by a tool or deployed to an environment. Common syntax errors include:

• Tab characters used instead of spaces for indentation (explicitly forbidden by the YAML spec)
• Inconsistent indentation levels within the same block
• Unquoted strings that parse as unexpected types — for example, yes, no, on, and off are interpreted as booleans in YAML 1.1
• Missing colons after mapping keys
• Invalid Unicode escape sequences

Catching these errors before deploying a Kubernetes manifest or a CI/CD pipeline config can save significant debugging time. Kubernetes and most CI systems provide cryptic errors when they receive malformed YAML; validating locally first narrows the problem immediately.

Common Use Cases

Kubernetes manifests are the highest-stakes YAML files most developers encounter. A single indentation error in a Deployment or Service manifest can cause kubectl apply to fail silently or produce a confusing API error. Pasting your manifest here before applying it to a cluster takes seconds and catches structural problems immediately. After validating, use our JSON to YAML converter if you need to generate manifests programmatically from JSON templates.

Docker Compose files are another common scenario. Compose uses YAML for service definitions, volumes, and networks. Errors in a Compose file can prevent containers from starting or cause ports and mounts to be configured incorrectly. Validating the file before running docker compose up prevents frustrating runtime surprises.

CI/CD pipeline configs — GitHub Actions workflows, GitLab CI, CircleCI, and Bitbucket Pipelines all use YAML. Pipeline syntax errors cause failed runs that waste build minutes and delay deployments. Validating the YAML structure here before pushing to the repository saves time and CI credits.

Ansible playbooks, Hugo and Jekyll site configs, and Helm chart values are additional file types where YAML validation catches problems early. For JSON-based configs, see our JSON Validator for the equivalent workflow. For more depth on YAML structure, read our YAML Tutorial.

Best Practices & Tips

Always use 2-space indentation. While YAML allows any consistent number of spaces, 2 spaces is the de facto standard across Kubernetes, Ansible, and most CI platforms. Mixing indentation levels (e.g., 2 spaces in one block and 4 in another) is a common source of subtle bugs.

Never use tabs. The YAML specification explicitly prohibits tab characters for indentation. Most editors can be configured to insert spaces when you press Tab — enable this for any file type associated with YAML (.yml, .yaml).

Quote strings that look like booleans or numbers. In YAML 1.1 (used by many tools), unquoted values like yes, no, true, false, on, and off are parsed as booleans, not strings. If you intend a string, wrap the value in quotes: "yes" or 'no'. Port numbers and version strings (e.g., 1.10) should also be quoted when a string is expected, to prevent them from being parsed as floats.

Validate before every deploy. Make YAML validation a mandatory step in your local workflow, not an afterthought. Many teams add a YAML lint step to their CI pipeline to enforce this automatically. For YAML validation best practices in production pipelines, see YAML Validation Best Practices.

Features

• Syntax Validation — Instant feedback with line numbers for errors
• YAML to JSON — Convert YAML to formatted JSON
• Multi-document Support — Handles YAML files with multiple documents
• Statistics — Shows key count, nesting depth, and document count

FAQ

What can this tool do?

Validate YAML syntax with detailed error messages, and convert YAML to JSON format.

Does it support multi-document YAML?

Yes. The validator can parse multi-document YAML files separated by ---.

Is my data safe?

Yes. All validation happens in your browser. No data is sent to any server.

Why does YAML reject my tab characters?

YAML forbids tab characters for indentation by specification. Only space characters are allowed. Replace all tabs with two or four spaces and the error will resolve.

What is the difference between YAML and JSON?

YAML is a superset of JSON designed for human readability. It uses indentation instead of braces and brackets, supports comments, and allows more data types like multi-line strings. JSON is stricter and better suited for machine-to-machine communication.