Express Lint is nine JSON and text tools on one site, all of which process your content in the browser rather than on a server. There is no account, no upload step and no server round trip for anything you paste.
JSON: validate with the exact line and column of the error, repair common mistakes in one click, beautify, minify, and explore a document as a collapsible tree with copyable JSONPaths.
Compare: character-level text diff, and a JSON diff that ignores key order and reports differences by path rather than by line, so reordered keys stop reading as changes.
Convert: JSON to YAML and back, and base64 encode and decode, each on a single page with a direction switch that carries the result straight back the other way.
Inspect: a JWT decoder for the header and payload.
There is also an 18-page reference for the JSON error messages people actually search for, across JavaScript, Python, Java, PHP and Go, each with a broken sample and the fix beside it.
The tools are built to be correct where the common ones are not. Base64 goes through UTF-8, so emoji, accented text and Chinese, Japanese and Korean characters survive a round trip; most online base64 tools use atob and btoa, which are latin1-only and mangle them silently. YAML follows the 1.2 rules, so "no" stays the string "no" rather than becoming false. JSON to YAML preserves key order and quotes strings that would otherwise change type. The JWT decoder decodes only and never asks for your signing secret, because pasting a signing secret into a web page is not something a decoder should require.
Page-view analytics are recorded and are described in full on the site's privacy page. Your pasted content is not part of them.
Omnideck added Express Lint as alternative to OmniDeck Pro
Express Lint 
