Diff Checker Online — Compare Two Texts and Highlight Differences Free

What Is a Diff?

A diff (short for "difference") is a structured comparison between two text inputs. The concept comes from the Unix diff command, developed in the early 1970s, which became foundational to version control. Today, diffs are the basis of every pull request review on GitHub, every tracked change in Google Docs, and every merge conflict in Git.

A diff checker presents this comparison visually, with added content highlighted in green and removed content in red, so you can see what changed without reading both texts in full.

How to Use the Diff Checker

1. Paste the original text. Add the first version of your text into the left panel — the "before" version.
2. Paste the changed text. Add the second version into the right panel — the "after" version.
3. Run the comparison. Click the Compare or Diff button. Differences are highlighted immediately: green for additions, red for deletions.
4. Review the output. Navigate through the highlighted changes. Lines that are the same in both versions appear unchanged; only lines with differences are marked.

Diff View Modes

Common Use Cases

Comparing code versions

Developers use diff checkers to compare two versions of a function, configuration file, or script before deploying a change. This is useful when you have a local copy and a production version and want to confirm exactly what differs before overwriting anything.

Document and contract review

Legal and business teams use diff checkers to compare contract revisions, policy documents, and terms-of-service updates. A word-level diff immediately shows which clauses were added, removed, or modified between drafts — saving hours of manual line-by-line review.

Configuration file comparison

System administrators and DevOps engineers compare config files (YAML, TOML, INI, JSON) between environments to catch discrepancies. A diff makes it immediately obvious if a production config file has diverged from the staging baseline. Pair the diff output with the JSON formatter to normalise JSON before comparing.

Plagiarism and content verification

Content teams and educators use diff checkers to compare submitted text against an original source to identify copying or paraphrasing. The diff shows which sections match exactly and which have been reworded.

Diff Algorithms

Most text diff tools use the Myers diff algorithm (1986), which finds the shortest edit script — the minimum number of insertions and deletions needed to transform one text into another. It is the algorithm behind git diff, GitHub's pull request view, and most Unix diff implementations.

For prose and natural language, patience diff and histogram diff produce more human-readable results by avoiding matching on common but uninformative lines (like blank lines or single-character lines). Git uses histogram diff by default for this reason.

Common Questions

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

Browser-based diff checkers process text locally without sending data to a server. The practical limit is determined by your device's memory and the browser tab's JavaScript heap. For most purposes — code files up to tens of thousands of lines, documents up to hundreds of pages — the tool handles the comparison without issue.

Does the diff checker ignore whitespace differences?

Many diff checkers offer an "ignore whitespace" option that treats differences in spaces, tabs, and line endings as non-differences. This is useful when comparing code that has been reformatted but not functionally changed, or documents that have been reflowed in a word processor.

Can I compare binary files or images?

No. Text diff checkers compare text content only. Binary files (PDFs, images, executables) cannot be meaningfully compared character by character. Specialised tools exist for image diffing (used in visual regression testing) and binary diff (used in reverse engineering and firmware analysis), but they operate on fundamentally different principles.