“Debugging”

Connects to a WebSocket server, sends messages and logs what comes back for debugging.

Shows what the compiler generates behind C++ features by expanding your code into explicit source.

SQLite playground for debugging and sharing SQL snippets, with the option to load your own data.

Displays key names and key codes for each key you press.

Decodes raw protobuf bytes without a schema and shows the field tree.

Opens an HTTP Archive file so you can inspect recorded requests and timings.

Decodes PHP serialize() strings, such as WordPress options or transients, into a readable nested dump.

Runs code step by step and draws the variables and memory at each line, for several languages.

Fetches a URL from the server side and shows its HTTP response headers, like a remote curl.

Shows incoming MIDI streams in color so you can see what a controller sends.

Compile, run and step-debug C, C++ and other languages with GDB in the browser.

Tests, explains and debugs regular expressions across several flavors such as PCRE2, JavaScript and Python, with code export.

Computes and visualises CSS selector specificity.

Online webhook tester that receives and inspects requests from services like Shopify and Slack.

Gives you a temporary URL and email address that records incoming HTTP requests so you can inspect webhooks.

Points at a remote MCP endpoint to browse the capabilities it exposes and try calling one with your own arguments.

Formats Java, Python, JavaScript and Go stack traces with automatic language detection.

Tests wss:// servers from the browser and shows incoming and outgoing frames.

Shows every format present on your clipboard after a paste, including text, HTML and images.

Builds an HTTP request from the browser and shows which response headers and body the page is actually allowed to read.

Displays the user agent string your browser sends along with an explanation of what it tells sites.

Draws a railroad diagram of a regex and highlights how it matches your sample text.

Decodes JSON Web Tokens and checks signatures, with libraries listed for many languages.