Diff Checker — Free Online Diff Tool
Paste or drop two snippets of text, code or documents and see every change highlighted instantly. Word, line and character-level diff with a side-by-side view — and unlike most online diff checkers, nothing ever leaves your browser.
No comparison yet. Paste or upload text in both fields below — results appear here automatically, and nothing is calculated until you do.
Compare your two texts
Original Text (A)0 words
Modified Text (B)0 words
What a Diff Checker Does
A diff checker takes two inputs — A and B — and identifies additions and removals. SnapTextCompare uses diff-match-patch with mode-specific grouping and cleanup. Added text is green, removed text red; cleanup groups edits for readability without promising a minimum edit script.
Diff checkers help answer "what changed?" in the supplied text. Check extraction and ignore settings, then review highlights in context; a text diff does not determine correctness or meaning.
Diff Modes
Word diff. Highlights changed words inside a line. Best for prose, configs and short scripts.
Line diff. Shows whole-line additions and deletions, unified-diff style. Best for source code and log files.
Character diff. Zooms into the changed characters within a word — perfect for catching a single-letter typo or a swapped digit in a contract number.
How the Diff Algorithm Actually Works
At the heart of every modern diff checker sits the longest common subsequence (LCS) problem: given two sequences, find the longest sequence of tokens that appear in both, in order. Everything not in the LCS is either a deletion (in A but not B) or an insertion (in B but not A).
Myers's O(ND) algorithm is one foundation of practical diffing. Performance depends on input length, change density, cleanup and rendering; this site does not claim a validated 50,000-line or millisecond benchmark.
Smart and Character modes compare characters; Word and Line encode runs or lines before diffing. Adjacent replacement spans receive character-level highlighting. The mode and ignore settings affect grouping and the resulting statistics.
SnapTextCompare vs Other Diff Checkers
Published by SnapTextCompare, not an independent benchmark. Other services vary by feature and plan; check their current offerings before choosing.
| Feature | SnapTextCompare | Diffchecker | Diffnow |
|---|---|---|---|
| Processing location | Local comparison | Varies by web/Desktop feature | Check feature policy |
| Free, no signup | ✅ | Limited (paid Pro) | ✅ |
| No ads | ✅ | ❌ | ❌ |
| PDF + Word upload | ✅ | Paid | ✅ |
| Export TXT / HTML / JSON | ✅ | Paid | Limited |
Diff Checker Use Cases
Code review. Compare two versions of a function without opening a PR.
Contract redlines. Verify only negotiated terms moved between drafts.
Copy editing. Show authors exactly what was changed in their draft.
Config debugging. Find the one line that broke production.
Prompt iteration. Compare two AI prompts (or two outputs) word by word.
API response diffing. Paste two JSON responses and instantly see which field changed between calls.
Email approval. Diff a marketing draft against the legal-approved version before scheduling the send.
Power-User Shortcuts
Paste & go. The tool diffs continuously as you type — no "Compare" button to click.
Ignore whitespace only when spacing is irrelevant. The tool does not distinguish logic from formatting, and whitespace can affect languages such as Python.
Ignore case when comparing email lists, SKUs, or anything where capitalisation drifts but content is identical.
Swap sides if you accidentally pasted the new version into the "original" side — one click reverses the highlighting.
Export JSON when you want to feed the diff into a CI pipeline, a Slack bot, or any downstream automation.
Related comparison tools
How SnapTextCompare compares source code
Diff engine
Google's diff-match-patch (Apache 2.0), running in your browser. Character mode diffs raw characters; word and line modes encode tokens or lines first and diff those, then decode the result.
Similarity & importance
Similarity = 1 − Levenshtein / max(len). Importance weighs each change by category — money and dates score 90+, punctuation scores 3. Fixed rules classify a given diff; they do not determine meaning or whether an edit is safe.
Privacy
Files are read with the HTML5 File API and processed in your browser. No network request is ever made with your content — verifiable in the Network tab of your browser's DevTools. Full recent comparisons are saved in this browser's local History, even after closing the tab. Clear History to remove them.
Code uses the shared text diff engine and a bundled set of highlight.js language grammars with heuristic detection. It compares text, not program behavior or syntax trees; use tests and repository review before merging.
Diff Checker FAQ
Common questions about online diff checkers.