Express Lint

Express Lint is a free set of ten developer tools for JSON and text. Every tool runs in your browser, so your data never touches a server. No account, no upload, no waiting.

Why people switch to it

Your data stays on your machine. API responses, tokens and customer records are processed locally. Paste production data without a second thought.

It handles big files. Validate and view JSON up to 50 MB without freezing the tab. Many online formatters give up at a few megabytes.

It fixes your JSON, not just rejects it. Get the exact line and column of the error, then repair trailing commas, single quotes, comments and unquoted keys in one click.

A JSON diff that understands JSON. Key order is ignored, type changes are called out, and every difference is listed by path. Reordered keys stop showing up as changes.

Correct where others break. Base64 handles emoji, accented text and Chinese, Japanese and Korean correctly. Many base64 tools mangle them or throw an error. YAML follows the 1.2 rules, so "no" stays a string instead of turning into false. CSV keeps leading zeros and long IDs intact, with an option that opens cleanly in Excel.

The tools

• JSON Validator with auto repair
• JSON Beautifier and Minifier
• JSON Viewer with a collapsible tree, a graph view, search and copyable paths
• JSON Diff with split, unified, tree and graph views
• Text Diff with character-level highlighting
• JSON to YAML and YAML to JSON
• JSON to CSV and CSV to JSON
• Base64 encode and decode, standard and URL-safe
• JWT Decoder that shows expiry dates in plain time and never asks for your secret

Also: 20 guides to the JSON errors people search for most, covering JavaScript, Python, Java, PHP and Go. Seven colour themes, including dark mode. Share links that keep your data in the URL fragment, which is never sent to a server.

Free, with no sign up. Page views are counted for analytics, as explained on the privacy page. What you paste is never part of that.