Free YAML Validator & Formatter Online
Catch indentation errors, duplicate keys, and tab-in-whitespace bugs before they break your GitHub Action, Kubernetes manifest, Docker Compose file, or Ansible playbook. Line-precise validation and a clean re-formatter — all 100% client-side.
Line-Precise Errors
When something is wrong, we tell you exactly which line and exactly what — tab in indentation, duplicate key, unexpected dedent, missing colon. No "syntax error" mystery messages.
Round-Trip Formatting
Parse to a structured tree, then re-emit clean YAML with consistent 2-space indent. Strip out trailing whitespace, normalize quote styles, and lock in formatting before you commit.
Catches the Norway Problem
YAML 1.1 famously turns `no` and `off` into booleans. We surface what your strings parsed as so you can quote them before a multi-million-row config file sets every country code wrong.
100% Client-Side
Parsing happens in your browser. Kubernetes secrets, deploy keys, Ansible vaults — paste them with confidence. Your YAML never reaches our servers, ever.
The Engineer's YAML Validator That Actually Says What's Wrong
YAML runs the modern cloud. Every Kubernetes manifest, every GitHub Actions workflow, every Docker Compose file, every Ansible playbook, every Helm chart — YAML. And yet the most common error message developers see is the same useless one: "syntax error: did not find expected key." Our Free Online YAML Validator & Formatter fixes that. We tell you the line, the column, and the reason — duplicate key, tab in indentation, unterminated quoted string, unexpected dedent. You fix once and move on.
Pair this validator with our JSON Formatter (every JSON file is valid YAML and our converter round-trips both directions), the CSV ↔ JSON Converter for tabular config exports, and the Cron Expression Builder to verify the schedules embedded in your GitHub Actions and Kubernetes CronJob YAML.
YAML vs JSON vs TOML: Which Config Format When?
| Attribute | YAML 1.2 | JSON | TOML |
|---|---|---|---|
| Human Readability | Highest | Moderate | High |
| Comments | Yes (#) | No | Yes (#) |
| Hierarchy | Indentation | Braces / brackets | [section.subsection] |
| Strict Spec | Loose (1.1 vs 1.2 differences) | Very strict | Strict |
| Best For | DevOps configs, CI pipelines | APIs, machine-to-machine | Application configs (Cargo, Hugo) |
The Five YAML Pitfalls Every Engineer Hits
1. Tab Characters in Indentation
YAML forbids tabs. Most "syntax error" reports from GitHub Actions are stray tabs from copy-paste. We flag them by line.
2. The Norway Problem
Unquoted no, off, yes, on become booleans in YAML 1.1. Quote country codes and similar atoms.
3. Leading Zeros = Octal
version: 010 parses as the integer 8. Always quote version numbers, ZIP codes, and IDs that may start with 0.
4. Inconsistent Indent Steps
Some children indented 2 spaces, siblings 4 — both are technically legal but visually misleading. Re-format with this tool before committing.
5. Duplicate Keys
YAML technically allows duplicate keys (later wins), but most parsers warn or fail. We hard-fail with the exact line.
Bonus: Colons Inside Values
url: https://example.com:8080 is fine, but label: a: b requires quoting. We surface ambiguous parses immediately.
A Production-Safe DevOps YAML Workflow
Validate Before Commit
Paste here. Fix line-precise errors. Run our re-formatter so diffs reflect logic, not whitespace.
Convert & Inspect
Use "Convert to JSON" to inspect the parsed structure in our JSON Formatter.
Verify Embedded Schedules
If your YAML carries a cron, lift it out and validate the schedule with our Cron Expression Builder.
Diff Against Production
Before merging, compare your formatted YAML to the live config with our Diff Checker.