A text diff (short for "difference") is a comparison between two pieces of text that identifies what was added, removed, or changed. Diff algorithms originated with the Unix diff utility in the 1970s and are the foundation of every modern version control system, including Git. The output highlights insertions, deletions, and modifications so you can review changes at a glance.

Line vs word vs character diff — when should I use each?

Line-level diff is best for source code and configuration files where each line is a distinct statement — it mirrors how Git and most code review tools display changes. Word-level diff is ideal for prose, documentation, and Markdown files where edits often touch individual words within a paragraph. Character-level diff is useful for spotting subtle typos, single-character bugs, or differences in minified code where every byte matters.

How does the diff algorithm work?

Most modern diff tools use the Myers diff algorithm , published by Eugene Myers in 1986. It finds the shortest edit script (the minimum number of insertions and deletions) to transform one sequence into another by searching an edit graph. The algorithm runs in O(ND) time, where N is the total length of both inputs and D is the size of the minimum edit script — making it extremely fast when the texts are similar. Variants like patience diff and histogram diff improve readability for specific cases like code refactoring.

Can I diff JSON or code specifically?

Yes. You can paste any text into the diff checker, including JSON, YAML, XML, SQL, or source code in any language. For JSON specifically, consider using our JSON Formatter & Validator to pretty-print and validate both documents before diffing — this normalizes whitespace and key ordering so the diff reflects only meaningful structural changes rather than formatting noise.

How do I read unified diff format?

In unified diff format, lines starting with - exist only in the original text (deletions), lines starting with + exist only in the modified text (additions), and lines with no prefix are unchanged context. A header like @@ -10,7 +10,8 @@ indicates the line range in each file. This format is the standard output of git diff and is widely understood by code review and CI/CD tools.

Is my data safe when using this diff tool?

Absolutely. All comparisons run entirely in your browser using client-side JavaScript — your text is never transmitted to a server. No data is stored, logged, or shared. This makes the tool safe for comparing proprietary source code, credentials files, or any sensitive content. For extra peace of mind, you can disconnect from the internet and the tool will continue to work offline.

Text Diff Checker

Free online text diff checker to compare and highlight differences with line, word, and character-level comparison

Mode:

Original

Modified

Enter text to compare

Frequently Asked Questions

JSON

Validate, format & convert JSON

Regex

Test patterns & matches

Markdown

Preview & export HTML

Hash

MD5, SHA, BLAKE2/3

Text Diff Checker

Original

Modified

Frequently Asked Questions

What is a text diff?

Line vs word vs character diff — when should I use each?

How does the diff algorithm work?

Can I diff JSON or code specifically?

How do I read unified diff format?

Is my data safe when using this diff tool?

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JSON

Regex

Markdown

Hash

Original

Modified

Frequently Asked Questions

What is a text diff?

Line vs word vs character diff — when should I use each?

How does the diff algorithm work?

Can I diff JSON or code specifically?

How do I read unified diff format?

Is my data safe when using this diff tool?