Diff Checker

What is Diff Checker?

Diff Checker is a free online tool that compares two pieces of text — or two JSON documents — and highlights exactly what changed between them. Added lines, removed lines, and untouched context are shown in a single inline view with line numbers from both versions, and modified lines get word-level highlighting so the precise change jumps out instead of hiding inside a long line.

Features

• Text mode — Classic line-by-line diff for code, configs, logs, or any plain text
• JSON mode — Parses both sides first, so you compare structure instead of raw formatting
• Sort keys — Optionally sorts JSON object keys recursively before comparing, so pure key-order noise disappears (arrays keep their order)
• Ignore whitespace — Treats lines that differ only in leading/trailing whitespace as unchanged
• Dual line numbers — Every row shows its line number in the original and the changed version
• Word-level highlights — Paired changed lines show the exact words that were added or removed
• Hide unchanged — Collapses long runs of identical lines into expandable summaries

How to use

Paste the original content on the left and the changed content on the right; the diff renders live below as you type. Switch between Text and JSON mode with the toolbar pills, toggle whitespace-insensitivity or key sorting as needed, and use Swap to flip the two sides. For very large inputs a Compare button appears so you control when the (heavier) diff runs.

Privacy

In the browser UI, all comparison runs locally on your machine — pasted content is not uploaded anywhere. (A public API endpoint exists for programmatic use; data you send to it is processed server-side to compute the diff.)