Guides
Short, practical, code-first explainers of how our tools actually work — the algorithms behind them, the gotchas to avoid, and copy-paste snippets you can use in your own projects. Every guide pairs with a free tool you can run right here in your browser.
- Lookups
How to find a company's EIN
Where a business's EIN is public and free — SEC filings for public companies, IRS data for nonprofits — plus the EIN format, EIN vs TIN/SSN/DUNS, and how to verify a private company's number.
- Lookups
How to decode a VIN by hand
The 17 characters explained in order — the WMI, VDS and VIS sections, the model-year and plant codes, and how to verify the check digit yourself, with a worked example.
- JavaScript
JSON in JavaScript: parse & stringify
How JSON.parse and JSON.stringify really work — pretty-printing, the replacer/reviver hooks, what JSON silently drops, and debugging SyntaxError.
- JavaScript
Hash a string with SHA-256 in JavaScript
The Web Crypto one-liner for SHA-256, converting the digest to hex, picking an algorithm, and why a plain hash is wrong for passwords.
- JavaScript
URL encoding in JavaScript
encodeURIComponent vs encodeURI, why URLSearchParams is the safest way to build query strings, and the +-versus-%20 space gotcha.
- JavaScript
Regular expressions in JavaScript
Literal vs RegExp constructor, test/match/matchAll/replace, the flags, capture and named groups, and the stateful /g lastIndex gotcha.
- JavaScript
Decode a JWT in JavaScript
Read a token’s header and payload with Base64url, check expiry from the claims, and why decoding a JWT is not the same as verifying it.
- Networking
How IP geolocation works
What an IP address really reveals about location, where the databases get their data, why results are city-level at best, and what throws them off.
- JavaScript
Base64 encode & decode in JavaScript
Why btoa/atob break on emoji, the UTF-8-safe fix, a tolerant decoder for URL-safe and unpadded input, and the Node way.
- JavaScript
Generate a UUID in JavaScript
The crypto.randomUUID() one-liner, a spec-compliant v4 fallback, why Math.random is wrong, and which version to use.
Looking for a tool rather than a guide? Browse the full tool list.