Validators

Check JSON, XML, HTML, emails, URLs, and cron expressions for correctness.

Before trusting a piece of data - a JSON payload, an XML document, an email address a user typed in, a cron expression meant to run on a schedule - it helps to know for certain whether it’s actually valid, not just whether it looks right at a glance. These tools check syntax and structure against the real rules each format requires, and point out specifically what’s wrong when something fails, rather than a generic error. Everything validates instantly and entirely in your browser, which matters when what you’re checking is a real payload, a user’s actual input, or something you’d rather not paste into an unfamiliar third-party site.

17 tools in this category

Color Contrast Checker

Check the WCAG contrast ratio between two colors, with pass/fail results for AA and AAA at both text sizes.

Credit Card Number Validator

Check a card number’s format with the Luhn checksum and detect its likely network.

Cron Expression Validator

Validate a 5-field cron expression and see its schedule described in plain English.

Email Validator

Check whether an email address is correctly formatted, with a plain-English reason when it isn’t.

IBAN Validator

Check an IBAN’s format and mod-97 checksum, with country/length and checksum shown separately.

ISBN Validator & Converter

Validate ISBN-10 and ISBN-13 checksums with auto-detection, plus convert between the two formats.

JavaScript Tester with Console

Run JavaScript in a sandboxed iframe and see console.log/warn/error output.

JavaScript Validator

Check JavaScript for syntax errors without running the code.

JSON Diff Checker

Compare two JSON values and see exactly which keys were added, removed, or changed - all client-side.

JSON Validator

Check whether JSON is syntactically valid, with the line and column of the error when the browser can pinpoint one.

JSONPath Tester

Test a JSONPath expression against your JSON and see exactly which values it matches.

Password Strength Checker

Check a password against length and character-variety rules, with a live strength meter - checked locally, never transmitted.

Phone Number Validator

Validate a phone number’s format for the US, UK, India, or international E.164 notation.

URL Slug Validator

Check whether a string is a valid, URL-safe slug and get a corrected suggestion if not.

URL Validator

Check whether a string is a valid URL and see it broken into protocol, host, path, and more.

XML Diff Checker

Compare two XML documents and see exactly what changed, ignoring formatting differences.

YAML Validator

Check whether YAML is syntactically valid, with a quick structure summary on success.