YAML Validator

How to use

1. 1Paste your YAML into the input box on the left. The validator runs in your browser as you type.
2. 2Read the green Valid banner or the red Invalid banner above the result panel. The red banner names the line and column of the first failure.
3. 3If invalid, open the Error location panel for a code snippet with a caret pointing at the bad character, and check the Likely cause hint for a plain-English explanation.
4. 4If valid, scroll down to Document breakdown for per-document summaries plus node counts, max depth, deepest path, and largest sequence and mapping sizes.
5. 5Click Copy error report to copy a self-contained, paste-ready description of the failure (location, hint, and a code snippet) when sharing the error with a teammate.
6. 6Try Load valid sample for a worked Kubernetes manifest stream, or Load broken sample to see how the validator reports a tab in indentation, a duplicate key, an unclosed flow collection, and an unterminated quoted string.

About this tool

YAML Validator is a single-purpose strict YAML checker. Paste any YAML document on the left and the tool tells you in plain English whether it parses as valid YAML 1.2 core schema. When the input is invalid it shows the exact line, column, and 0-based byte index of the failure, draws a code snippet with the surrounding lines, marks the bad character with a caret pointer, and adds a Likely cause hint that explains the most common cause in plain English. The hint engine recognises tab characters in leading indentation (forbidden by the spec), duplicate mapping keys inside the same block or flow mapping, misaligned sibling keys and sequence items, unterminated single- or double-quoted strings (including inside flow collections), invalid escape sequences in double-quoted strings (\x \u \U and the standard letter escapes), unclosed flow collections like [a, b, c and {k: v, sequence markers without the required space after - so -value is correctly flagged as a plain scalar rather than a sequence item, aliases (*name) that reference an anchor that was never defined, smart or curly quotes pasted from word processors, and a UTF-8 byte order mark at the very start of input. When the input parses, the tool reports a per-document summary plus a global breakdown: document count, root type per document, total node count, max nesting depth, mapping / sequence / scalar counts, scalar type distribution (strings, numbers, booleans, nulls), total and unique key counts, the deepest dotted key path in the tree, the largest sequence, and the largest mapping. The parser covers the YAML 1.2 subset that real config files use: block mappings and block sequences with any consistent leading indent, plain / single-quoted / double-quoted scalars with full escape support, flow-style [a, b] and {k: v} with nested values, literal | and folded > block scalars with all three chomping indicators, anchors (&name) and aliases (*name), multi-document streams with --- separators and ... end markers, and trailing # comments. Useful for catching the indentation drift that breaks Kubernetes apply, finding the duplicate key that makes a GitHub Actions workflow ignore half your steps, spotting the missing closing bracket in a Docker Compose flow value, and confirming that an Ansible playbook or OpenAPI spec parses cleanly before commit. Everything runs locally in the browser; nothing is uploaded, logged, or sent to a server.

Free to use. Works in your browser. No signup, no login.