Code and Data Validation Tools
Find syntax and structure problems before they reach an API, build, deployment or production page. Each validator explains the result next to your input.
Choose a tool
18 browser-based tools are available in this collection. Open a tool to see its input, output and current size limit.
JSON Validator
JSON Validator is a browser-based tool for validating JSON syntax. Paste your input, review the result, and…
Email Validator
Email Validator is a browser-based tool for validating Email syntax. Paste your input, review the result…
Free Online HTML Validator
HTML Validator is a browser-based tool for validating HTML syntax. Paste your input, review the result, and…
Free Online YAML Validator
YAML Validator is a browser-based tool for validating YAML syntax. Paste your input, review the result, and…
XML Validator
XML Validator is a browser-based tool for validating XML syntax. Paste your input, review the result, and…
Free Online CSS Validator
CSS Validator is a browser-based tool for validating CSS syntax. Paste your input, review the result, and…
Free Online SQL Validator
SQL Validator is a browser-based tool for validating SQL syntax. Paste your input, review the result, and…
RSS Validator
RSS Validator is a browser-based tool for validating RSS syntax. Paste your input, review the result, and…
CSV Validator
CSV Validator is a browser-based tool for validating CSV syntax. Paste your input, review the result, and…
Free Online UUID Validator
UUID Validator is a browser-based tool for validating UUID syntax. Paste your input, review the result, and…
Regex Tester
Test regex online
Browser-only tools
JSONL Validator
Validate, format and convert JSON Lines in your browser.
.env Validator
Check .env files for common syntax mistakes and format them safely in your browser.
JSON Schema Validator
Validate JSON against a practical browser-based JSON Schema subset.
File Hash Checker
Calculate SHA-1, SHA-256, SHA-384 or SHA-512 checksums locally in your browser.
JSON Duplicate Key Checker
Find duplicate object keys that a normal JSON parser may silently overwrite.
.gitignore Tester
Test common .gitignore patterns against file paths in your browser.
File Type Inspector
Inspect a file name, extension and common magic bytes locally in your browser.
Privacy-first developer workflows
Supported input is processed in the browser, so source data does not need to be uploaded to a server. Limits vary by tool and browser; the tool page shows the relevant behavior before you start.
How to choose the right tool
Use formatters and beautifiers when code is difficult to read, validators when you need to find syntax problems, and converters when another system expects a different data structure. For production bundles, use a minifier only after reviewing the readable source and testing the result.
Bookmark this collection for repeat debugging, API inspection, configuration review and data-cleanup tasks. Every tool links to adjacent workflows so you can move from validation to formatting or conversion without returning to the home page.