Validate YAML text and files
YAML breaks when indentation is wrong. This validator finds spacing mistakes, missing colons, and structure problems before deployment. Paste your YAML and get line-by-line error reports. All processing happens in your browser.
What happens when you validate YAML
Code scanning
The validator reads each line of your YAML file. It counts spaces at the start of lines to check indentation levels. It looks for colons after keys and spaces after list dashes.
Error detection
Problems get flagged immediately. Tabs mixed with spaces trigger errors. Missing spaces after colons get reported. Unclosed quotes show up with line numbers.
Report generation
You see a list of errors with exact line numbers. Each error explains what is wrong and where to fix it. Valid files show a success message.
Four types of YAML errors you will encounter
Indentation mistakes
YAML uses spaces for structure. Mixing tabs with spaces breaks parsing. Using 3 spaces instead of 2 or 4 causes problems. Child elements must align with parent indentation levels.
Syntax violations
Keys need colons followed by spaces. Writing
name:valueinstead ofname: valuetriggers errors. Unclosed quotes and duplicate keys at the same level get flagged.Structure issues
Lists require dashes with spaces. Writing
-iteminstead of- itemfails validation. Nested objects must maintain consistent indentation relative to their parents.Formatting problems
List items need proper spacing after dashes. Multi-line strings require correct indentation. Special characters in unquoted strings cause parsing failures.
When developers use this validator
Checking docker-compose.yml before running containers
Docker Compose files fail silently when YAML syntax is wrong. A missing space after a colon stops services from starting. Copy your docker-compose.yml content into the editor. Click Validate YAML. Fix errors like inconsistent indentation or missing colons. Re-validate until clean. Deploy with confidence.
version: '3.8'
services:web:image: nginx:latest
ports:- "80:80"
database:image: postgres:13
environment:POSTGRES_DB: myapp_dbResult: Validator confirms well-formed structure, preventing runtime parsing errors.
Validating Kubernetes manifests before kubectl apply
Kubernetes rejects YAML files with syntax errors. A single tab character breaks deployment. Open your deployment.yaml file. Paste the entire content into the validator. Review reported indentation problems. Replace tabs with spaces. Fix missing colons. Validate again. Apply to your cluster once validation passes.
apiVersion: apps/v1
kind: Deployment
metadata:name: my-app
spec:replicas: 3
template:spec:containers:- name: app-container
image: my-app:1.0.0Result: Validator confirms proper indentation and structure, preventing cluster deployment failures.
Testing GitHub Actions workflows before commit
GitHub Actions workflows fail when YAML structure is invalid. Missing list indicators break pipeline execution. Open your .github/workflows/main.yml file. Copy the workflow definition. Paste into the validator. Check for missing dashes in step lists. Fix incorrect nesting. Re-validate. Commit once the validator reports success.
name: CI/CD Pipeline
on:push:branches: [ main ]jobs:build:runs-on: ubuntu-latest
steps:- uses: actions/checkout@v2
- name: Run tests
run: npm testResult: Validator confirms workflow structure matches YAML standards.
How to validate your YAML files
Paste your YAML code
Open your YAML file in a text editor. Select all content and copy it. Paste into the editor on this page. You type directly if you prefer.
Start validation
Click the Validate YAML button. Validation runs automatically after you stop typing for one second. Watch the results panel on the right.
Read error messages
Valid files show a green success message. Invalid files list errors with line numbers. Each error explains what is wrong.
Fix problems
Use line numbers to find errors in your code. Replace tabs with spaces. Add missing colons. Fix indentation. Correct unclosed quotes.
Validate again
Click Validate YAML after making changes. Repeat until the validator reports no errors. Your YAML file is ready to use.
Who benefits from this YAML validator
Backend Developers
Validate configuration files and API response formats before deployment
DevOps Engineers
Check Docker Compose files, Kubernetes manifests, and CI/CD configurations
QA Engineers
Test YAML parsing in applications and report format issues
Data Engineers
Verify exported YAML files meet format requirements for data pipelines
System Administrators
Validate infrastructure configuration files and deployment manifests
What this validator does and what it does not do
Runs entirely in your browser
Your YAML code never leaves your computer. Validation happens locally. No data gets uploaded to servers.
Shows errors immediately
Errors appear with line numbers as you type. Fix problems right away instead of waiting for deployment failures.
Catches indentation problems
Finds tabs mixed with spaces. Reports inconsistent spacing levels. Flags wrong nesting immediately.
Does not validate schemas
This tool checks syntax only. It does not validate against JSON Schema definitions. Use schema validators for that.
Slows down with large files
Files over 1MB make the browser sluggish. Break large YAML files into smaller pieces and validate each part.
Requires spaces not tabs
YAML specifications require spaces for indentation. Tabs cause validation errors. Most editors convert tabs automatically.
YAML writing tips and mistakes to avoid
Pick one indentation size and stick with it
Choose 2 spaces or 4 spaces for your entire file. Do not mix sizes. Consistent spacing prevents parsing errors.
Add spaces after colons
Write name: value not name:value. The space after the colon is required in YAML.
Quote strings with special characters
Strings containing colons, spaces, or special symbols need quotes. Unquoted strings break when they contain these characters.
Format lists with dashes and spaces
Write - item with a space after the dash. Writing -item or - item causes errors.
Do not use tabs
Tabs break YAML parsing. Use spaces only. Configure your editor to insert spaces when you press Tab.
Do not mix single and double quotes
If you start a string with a single quote, end it with a single quote. Starting with double quotes requires ending with double quotes.
How this validator processes YAML files
JavaScript code runs in your browser to check YAML syntax. The validator follows YAML 1.2 rules for structure and formatting. It reads your code line by line. Each line gets checked for proper indentation using space counts. Key-value pairs require colons followed by spaces. Lists need dashes with spaces after them. Quote characters get counted to find unclosed strings. Duplicate keys at the same indentation level get flagged. Tabs trigger errors because YAML requires spaces. The Ace editor adds color highlighting to make code easier to read. Validation runs automatically one second after you stop typing. All checking happens locally in your browser. No data gets sent to servers.
What this validator checks and what it misses
- The validator follows YAML 1.2 rules for syntax and structure. It does not check against JSON Schema definitions. Use separate schema validation tools for that.
- Files larger than 1MB slow down browser processing. Break large YAML files into smaller sections and validate each part separately.
- Indentation checking confirms spacing consistency. It does not verify that nested data makes logical sense for your use case.
- Error line numbers point to approximate locations. Multi-line strings span multiple lines, so line numbers serve as starting points for fixes.
- Quote checking finds unclosed strings. It does not validate escape sequences inside quoted strings. Check escape sequences manually if needed.
About the Toolexe team
Toolexe creates validation tools for developers working with configuration files and data formats. Our team includes engineers with experience in DevOps, containerization, and infrastructure automation. We update this validator weekly to match YAML specification changes. Last review date: January 31, 2026. Reviewed by Toolexe QA team member JH. Report bugs or suggest improvements through the Contact Us page.
Your data stays private. All validation runs in your browser. No server uploads occur. Error messages explain problems clearly. Validation rules follow published YAML specifications.
