YAML Validator
Validate YAML syntax and catch duplicate keys, tab indentation, and multi-document errors with line/column detail — then fix them with one click.
What is YAML Validation?
YAML validation checks whether a document follows correct YAML syntax and flags the structural mistakes that syntax checking alone misses — duplicate mapping keys and tab characters used for indentation. Since YAML relies on whitespace rather than brackets to express structure, small indentation mistakes are the most common way a document silently changes meaning or fails to parse.
Unlike a YAML formatter, which re-indents already-valid YAML, a YAML validator checks correctness without changing your data. It reports every problem it finds — the parser's own syntax error, any duplicate keys, and any tab-indented lines — each with a precise line and column, so you can fix every issue in one pass instead of hitting them one at a time.
This is especially useful for YAML that a parser will happily accept but that doesn't mean what you think: when the same key appears twice in a mapping, most YAML libraries silently keep only the last value and discard the first, with no warning. This tool catches that case explicitly, alongside real syntax errors and indentation problems.
This page lets you validate YAML online for free, directly in your browser. Paste any YAML — or drag and drop a .yaml/.yml file — and click Validate to get a pass/fail result with a full, line-numbered list of every issue found. When something is wrong, click Fix Issues to fix duplicate keys and tab indentation automatically, without leaving the page. Everything runs locally; your YAML is never sent to a server.
Automatically Fix YAML Issues
Finding an issue is only half the job — this validator can fix the mechanical ones for you. After validating, a Fix Issues button appears next to Download Report whenever the file has at least one auto-fixable problem. Click it to reveal a fix action next to each duplicate-key or tab-indentation issue in the list.
Duplicate Key → Remove Line
Deletes the repeated key, keeping the first occurrence — the value you originally intended, not whichever one a parser would silently keep.
Tab Indentation → Fix Tabs
Converts the leading tab characters on that line to spaces, resolving both the indentation issue and the syntax error it usually causes.
Fix All
Applies every automatic fix across the whole file — including every document in a multi-document file — in a single click, then re-validates.
Syntax errors — an unclosed bracket, a bad colon, invalid nesting — aren't offered a fix button, since there's no single safe way to guess what was intended. Those are marked Manual fix in the issue list so you know exactly which lines still need a look. Every fix re-validates the document immediately, so you can keep clicking Fix All until only manual issues remain.
Why Validate YAML?
Catch Broken Manifests Before Deploy
A single misindented line in a Kubernetes manifest or CI workflow can silently break a deploy. Validating first catches it before it reaches a pipeline.
Avoid Silent Data Loss
Duplicate keys in a YAML mapping are not a syntax error to most parsers — the earlier key is silently discarded. This is easy to introduce by copy-pasting config blocks and easy to miss by eye.
Fix the #1 YAML Footgun
Mixing tabs and spaces in indentation is invalid YAML and the most common cause of confusing parser errors. This validator points to the exact tab character causing the problem — and can fix it for you.
Review Multi-Document Files
Kubernetes manifests and CI configs often bundle several resources in one file separated by ---. Each document is validated on its own, so one broken document does not hide errors in the others.
Example
Here's valid YAML alongside the same mapping with a duplicate key — a mistake most parsers accept silently but this validator flags explicitly.
apiVersion: apps/v1
kind: Deployment
metadata:
name: web
labels:
app: web
spec:
replicas: 3
template:
spec:
containers:
- name: web
image: nginx:1.25
ports:
- containerPort: 80user:
id: 42
name: Jane Doe
email: jane@example.com
id: 43Features
Validate Syntax
Parse YAML and surface every syntax error with its exact line and column.
Duplicate Key Detection
Catch repeated mapping keys explicitly, since YAML parsers silently keep only the last one by default.
Tab Indentation Check
Flag tab characters used for indentation — YAML's most common footgun.
One-Click Auto-Fix
Remove duplicate keys and convert tabs to spaces automatically, one issue at a time or all at once.
Multi-Document Support
Validate every ---separated document in a file independently and report issues for each.
Upload a File
Drag and drop or upload a .yaml/.yml file to validate it directly.
Copy / Download Report
Export the full list of issues as a report you can share or attach to a PR.