Code Testing — 17 Free Online Tools
Test regex patterns, JWT tokens, grammar, text diffs, math and typing speed. Built for everyday coding workflows, with instant feedback.
Paste something in, get an answer you can act on. The ReDoS Checker measures what a pattern costs when a match fails and hands back the string that breaks it, the Regex Tester reports capture groups and match indices, the JWT Decoder shows header and payload separately so a signing fault is distinguishable from a bad claim, and the Online Code Runner executes Python, JavaScript and HTML so you can check a snippet before it reaches your codebase.
Code Minifier & Beautifier - JS, CSS, HTML
Free online code minifier and beautifier. Minify JS, CSS, HTML for production or beautify for debugging. Size stats, copy, all in browser. No signup.
Cron Expression Evaluator & Explainer
Paste a cron expression and get its plain-English meaning, the next 10 run times in your timezone, and the traps that break it silently.
cURL to Code Converter - Python, Node, Go, PHP, C#
Convert curl commands to Python, Node, Go, PHP, or C# code. Deterministic parser, 100% in-browser, no upload, no signup, and free to use forever.
Free Grammar Checker - AI Error Explanation
Free AI grammar checker that not only corrects your English but explains why it's wrong. Perfect for learning proper grammar rules.
Free Online Math Solver - Step-by-Step Solutions
Free online math solver with step-by-step solutions. Solve algebra, equations, fractions, and more. No signup required, instant results.
Free Text Diff Checker - Compare Text & Code Online
Free online text diff checker to compare text and code. Side-by-side view with syntax highlighting. Compare JSON, XML, code files and find differences.
Free Typing Test - WPM, Accuracy & Code Mode
Free online typing test with WPM, accuracy and code snippet modes (JavaScript, Python, SQL, HTML). Practice words, quotes, numbers and syntax. No signup.
htaccess Redirect Tester - Test Rewrite Rules Online
Free htaccess redirect tester. Paste .htaccess rules and a URL, see which rule matched and why, and get the corrected line for the mistake.
HTML Playground - Live Code Editor Preview
Free HTML playground with live preview. Write and test HTML, CSS, JavaScript code instantly in your browser. No signup, 100% private.
JavaScript Obfuscator - Protect JS Code Online
Free online JavaScript obfuscator. Protect your JS code with variable renaming, string encryption, control flow flattening, and more. 100% private browser.
JWT Decoder - Decode & Verify Tokens
Free JWT decoder. Inspect the header and claims of any token, check the expiry, and see which algorithm signed it. Nothing is transmitted.
JWT Generator - Create Signed Tokens Online
Free JWT generator. Create signed JSON Web Tokens with HS256, HS384, HS512 algorithms. No signup, no upload, 100% private browser processing.
Log File Merger - Merge Logs by Timestamp Online
Merge many log files into one timeline ordered by the real time of each line. Per source timezone override, correlation window and silence gaps.
Online Code Runner - Python, JavaScript, HTML
Free online code runner. Run Python, JavaScript, and HTML/CSS in your browser. Real Pyodide WASM Python, sandboxed JS Web Worker, live HTML preview.
ReDoS Checker - Regex Denial of Service
Find catastrophic backtracking in any regex. Static shape analysis plus a measured growth curve in a Web Worker, and the attack string that triggers it.
Regex Tester - Test Regular Expressions
Test regular expressions against your own text with live highlighting. Supports the g, i, m, s, u and y flags, shows every match and capture group.
SemVer Conflict Solver - npm Version Range Checker
Check whether npm semver ranges resolve together. Finds the conflicting constraints, shows what each range allows, and names the newest published match.
Frequently Asked Questions
4 Q&AWhat can I test with the code testing tools?
You can validate regular expressions against sample text, decode and verify JWT tokens (HS256/RS256), check grammar, diff two text blocks, solve math problems step-by-step, and measure typing speed. All 17 tools are free, no signup.
How does the regex tester work?
Paste a regex and a test string; the tool highlights all matches in real time and reports capture groups, indices, and flag behavior (global, case-insensitive, multiline). Patterns execute in your browser using the JavaScript RegExp engine.
Is the JWT decoder safe to use with real tokens?
Yes for inspection: decoding only reads the header and payload, it does not verify the signature. Do not paste tokens containing highly sensitive claims (PII, secrets) into any third-party site; for production verification, use a library in your own backend.
Do these tools require an account or API key?
No. All 17 code-testing tools run client-side with no server API calls and no signup. You can use them offline once the page is loaded.
How to Use These Code Testing Tools
guideEvery code testing tool below runs entirely in your browser — no signup, no upload, no watermark. To find a specific tool, type a name, keyword, or scenario into the search box and the list filters instantly. Popular code testing tools are linked in the summary at the top; click any card or link to open the tool and follow the on-screen instructions. Hover any tool card to read its full description, then click its name or button to open it.