Free online developer tools

x86 PC emulator in WebAssembly that boots Linux, KolibriOS and older Windows.

Interactive Python console that runs CPython compiled to WebAssembly inside the page.

Bundles, minifies and compresses npm packages in the browser to show gzip and brotli size.

Parses DER, BER and PEM data such as certificates and keys into a readable ASN.1 tree.

Offline-capable viewer of tldr-pages command cheat sheets that runs in the browser.

Auto-detects pasted strings such as JWT, JSON, base64, URI, timestamp or gzip and shows the decoded view.

Explains a cron expression in plain words, field by field, and lists the next ten run times.

Moves the CSS you paste into inline style attributes on the HTML, the format email clients expect.

Converts CSS pixel values to rem and back.

Rewrites the variables of a .env file as entries for a netlify.toml configuration.

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

Previews pasted HTML in a sandbox, can run scripts, copy as PNG and make a share link.

Indents and structures raw JSON for reading and validation.

Validates JSON Lines files, such as AI datasets and event logs, and jumps to the failing line.

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

Turns a URL query string into a JSON object.

Tests a regular expression with flags against sample text, shows match counts and supports replace.

Generates random UUIDs.

Generates random UUID v4 values with options for hyphens and uppercase.

Fetches a GitHub repository and merges its files into one text file for pasting into an LLM.

Decodes Base64, Gzip and JWT tokens and formats the JSON inside, all client-side.

Fill a grid and set column alignment to get a Markdown table, with offline use and no uploads.

Reads a cluster snapshot, flags over-provisioned workloads and estimates the wasted spend.

Formats, validates and minifies JSON in the browser, with 2 or 4 space indents.