Validate YAML Syntax Instantly
Paste YAML or upload a .yaml/.yml file and the validator parses the document with a full YAML 1.2 parser, reporting either success with the parsed value rendered as JSON, or the exact line and column of the first syntax error along with a description of what the parser expected. Validation re-runs on every keystroke so you can fix errors incrementally.
YAML's indentation-driven structure makes subtle mistakes easy and hard to spot: a space in the wrong column, a tab mixed with spaces, an unquoted string that starts with a yes/no/on/off keyword, a block that silently becomes a flow, a duplicate key. This tool catches each of these with a specific error message, which saves the round-trip of pushing to CI only to find out a Kubernetes manifest, Docker Compose file, GitHub Actions workflow, CircleCI config, Ansible playbook, or OpenAPI spec is malformed.
Multi-document YAML separated by --- delimiters is fully supported: each document is validated independently and the parsed result becomes an array of document values. A JSON preview of the parsed structure appears below the editor so you can confirm not just that the syntax is valid but that it parsed to the data you expected — catching semantic bugs (wrong types, unintended null, key ambiguity) that pure syntax validation would miss.
Everything runs locally — your YAML, which often contains environment names, hostnames, or image tags, never reaches a server.
About YAML validation
YAML is a human-readable data serialization format used for configuration files (Docker Compose, Kubernetes, CI/CD). Syntax errors in YAML can be hard to spot due to indentation-based structure.
- Real-time validation as you type
- Error messages with line and column numbers
- Parsed JSON output preview
- Multi-document YAML support (--- separators)
- Upload .yaml/.yml files
100% client-side. Your inputs never leave your browser. Ads via AdSense (consent required).
Frequently asked questions
How do I validate YAML syntax?
Paste a YAML document and the validator parses it with a YAML 1.2-compliant parser and reports any syntax errors with line and column numbers. Common issues like inconsistent indentation, unclosed flow sequences, tab characters where spaces are required and bad anchor references are flagged with a human-readable reason. If the document is valid, you get a green check plus a count of keys and depth.
Is the YAML validator free?
Yes, fully free with no signup. Validate unlimited documents — Kubernetes manifests, GitHub Actions workflows, Ansible playbooks, docker-compose files. JSONCraft is free across every tool including this one; no premium tier gating rules. Useful in a pre-commit workflow or during review of config PRs.
Does the validator upload my YAML?
No. Validation runs entirely in your browser. Nothing is transmitted — crucial for YAML files that contain secrets, TLS certificates or cluster endpoints. You can validate a sealed-secrets.yaml before applying it without any byte leaving your machine; there is no history, no account and no logging.
What YAML spec does it validate against?
YAML 1.2, the current standard. It accepts 1.2's stricter rules (no more 'no' parsing as false by default, explicit nulls, fewer implicit typings) and flags the common YAML 1.1 habits that 1.2 rejects. Tab characters in indentation are an error regardless of version (YAML forbids tabs for indent). Custom tags beyond the core schema are allowed syntactically but not type-checked.
Does validation check schema or just syntax?
This validator checks YAML syntax only — is the document a well-formed YAML parse tree? It does not know whether keys and values match an expected schema (a Kubernetes Pod spec, a GitHub Actions workflow). For that, use a schema-aware linter like kubeval, actionlint or the JSON Schema validator tool. Syntax validation here is the fast first gate; schema validation is the deeper second pass.
Sources (1)
- Ben-Kiki, O., Evans, C., & döt Net, I. (2021). YAML Ain't Markup Language (YAML™) version 1.2, Revision 1.2.2. YAML Language Development Team (yaml.org), October 2021.
These are the specifications and standards this tool implements.
By Marco B. ·