Is there a size limit?

No hard limit, but very large texts (over 1MB) may be slow since processing happens in your browser.

Yes. The monospace font and line-by-line comparison works well for code diffs.

Does it detect character-level or just line-level changes?

Both. Diffs are computed at the character level using the diff-match-patch algorithm (the same one behind Google Docs edits). You will see exact insertions and deletions within a line, not just whole-line replacements.

Does it treat whitespace and indentation as meaningful?

Yes. A change from tabs to spaces or a 2-space vs 4-space indent shows up as a diff. If you want to ignore whitespace changes, normalize both inputs first.

Is there a size limit on the text I can compare?

No hard cap, but both inputs stay in memory and rendering slows past several thousand lines. For very large diffs, consider a command-line tool like `diff` or Git.

Diff Checker & Text Compare Online — Find Differences Free

Compare two blocks of text side by side and instantly see the diff — additions, deletions, and modifications highlighted. Also known as text compare.

When you need a diff checker

A diff checker (also called a text compare tool) highlights exactly what changed between two pieces of text. Common scenarios:

Code review — paste two versions of a function to see what the PR actually changed, without the noise of a full-repo diff.
Config auditing — compare a production config with a staging config to find the one line that's different.
Deployment verification — diff a generated file before and after a deploy to confirm only expected changes went out.
Content editing — compare two drafts of a document to see exactly what was added, removed, or reworded.
Data validation — compare an API response before and after a migration to confirm data integrity.
Debugging — paste expected output vs actual output and let the diff tell you what's wrong.

If you've ever found yourself squinting at two blocks of text trying to spot the difference — that's what this tool solves.

How the diff algorithm works

This tool uses the diff-match-patch library, which implements Eugene Myers' O(ND) difference algorithm — the same algorithm behind Google Docs' collaborative editing and many Git diff implementations. Here's what that means in practice:

Character-level precision — the diff operates at the character level, not just line-by-line. If you change one word in a sentence, only that word is highlighted — not the entire line.
Minimal edit distance — the algorithm finds the smallest set of insertions and deletions needed to transform one text into the other. This produces clean, readable diffs.
Real-time processing — diffs are computed instantly as you type or paste, with no round-trip to a server.

Green marks additions (text in the right/new version that wasn't in the left/old version). Red marks deletions (text in the left/old version that was removed). Unchanged text appears with no highlight.

Diff checker vs text compare vs file diff

These terms refer to the same core operation — finding differences between two inputs. The naming varies by context:

Diff checker — the generic term, most common in developer circles. Usually implies a paste-in tool.
Text compare — the same thing, more common in non-developer contexts (technical writing, legal review, content editing).
File diff — compares entire files, usually with line numbers and hunk headers. Tools like diff, git diff, and vimdiff work this way.
JSON diff — a structural comparison that understands JSON semantics (key order doesn't matter, nested paths are shown). See our JSON Diff tool for that.

This tool handles plain text and code. If you're comparing JSON specifically, use JSON Diff for a more meaningful structural comparison.

Tips for cleaner diffs

Normalize whitespace first. Trailing spaces and mixed line endings (CRLF vs LF) create noisy diffs. If you only care about content changes, strip trailing whitespace from both inputs before comparing.
Sort unordered data. If comparing two lists where order doesn't matter, sort both alphabetically first so the diff shows actual content differences, not reordering noise.
Use the right tool for structured data. For JSON, use JSON Diff which understands key semantics. For CSV, compare the data columns, not the raw text. For XML, use a structural differ.
Redact sensitive data. If you're sharing a diff with someone, replace API keys, tokens, and passwords with placeholders first. This tool runs in your browser so nothing leaves your device, but screenshots and copy-paste can leak secrets.

Command-line alternatives

This tool is great for quick, visual diffs. For more advanced needs:

diff file1.txt file2.txt — the Unix standard. Add -u for unified format (the most readable).
git diff — built into Git, understands file renames, binary files, and submodules. Add --word-diff for inline word-level changes.
delta — a modern diff viewer with syntax highlighting, line numbers, and side-by-side mode. Drop-in replacement for git diff.
jq — for comparing JSON files, pipe through jq -S to sort keys before diffing.

Related comparison tools on CodeBoxTools

JSON Diff — structural comparison of two JSON objects with path-level change tracking.
Word Counter — count words, characters, and sentences in your text.
Regex Tester — test and debug regular expressions with match highlighting.

Diff Checker — Text Compare Online