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YAML Validator

Paste YAML and instantly see if it's valid. Errors show the exact line and column number. Valid YAML displays the root type, key or item count, and byte size.

Last updated: May 21, 2026

Client-Side Processing
Input Data Stays on Device
Instant Local Execution

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What is YAML Validator?

YAML (YAML Ain't Markup Language) is a human-friendly data serialization format used widely in configuration files — Kubernetes manifests, GitHub Actions workflows, Docker Compose files, Ansible playbooks, and more. Despite being designed for readability, YAML has strict indentation rules and several syntax gotchas: tabs are not allowed for indentation, colons in unquoted strings can cause unexpected parsing, and special characters in values need quoting.

This validator uses the js-yaml parser to check your YAML against the full specification. Errors include the exact line and column where parsing failed so you can jump straight to the problem. For valid YAML, it shows the root type (mapping, sequence, or scalar), the number of top-level keys or items, and the byte size.

How to Use YAML Validator

1

Paste YAML into the input area or click "Valid Sample" or "Invalid Sample"

2

The validator runs instantly

3

A green badge means the YAML is valid; red means invalid

4

If invalid, the exact line and column of the error is shown

5

Fix the issue and re-validate

Common Use Cases

  • DevOps engineers validating Kubernetes manifests before applying with kubectl.
  • Developers checking GitHub Actions workflow files before committing.
  • Teams validating Docker Compose files before running docker-compose up.
  • Engineers verifying Ansible playbooks before running against infrastructure.
  • Developers debugging YAML parse errors in CI/CD pipelines.
  • Students learning YAML syntax by checking whether their YAML is correctly structured.

Example Input and Output

A YAML file with a tab character used for indentation (invalid in YAML) fails validation with a precise line number.

Invalid YAML
server:
  host: localhost
	port: 8080
Validation result
✗ Invalid YAML
found character that cannot start any token at line 3, column 1

Fix: replace the tab with spaces — YAML does not allow tab indentation

Privacy

All validation runs in your browser using js-yaml. No data is uploaded to any server.

YAML versions

This validator uses js-yaml which implements YAML 1.2. Some YAML 1.1 features differ slightly — notably, YAML 1.1 interprets yes/no/on/off as booleans while YAML 1.2 does not. If your toolchain uses YAML 1.1 (older Ruby, Python PyYAML default), results may differ.

Frequently Asked Questions

Why does YAML not allow tabs for indentation?
The YAML specification explicitly forbids tab characters for indentation because tab width is ambiguous (different editors display tabs differently). Use spaces only. Most editors can be configured to insert spaces when you press Tab.
My YAML looks fine but still fails — what should I check?
Common YAML pitfalls: (1) Colons in unquoted values — wrap in quotes: "key: value". (2) Special chars like #, :, >, | at the start of a value need quoting. (3) Inconsistent indentation depth. (4) Boolean-like strings (yes, no, on, off, true, false) parsed as booleans unless quoted.
What does "mapping" vs "sequence" mean in the stats?
YAML uses its own terminology. A mapping is an object (key-value pairs, like JSON {}). A sequence is an array (list of items, like JSON []). A scalar is a single value: string, number, boolean, or null.
Is my YAML sent to a server?
No. All validation runs in your browser using the js-yaml library. Your YAML never leaves your device.

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