Text Diff Checker

Compare two texts and find differences instantly. See what was added, removed, or changed line by line.

About the Text Diff Checker

Compare two versions of text side by side and instantly see every change — additions (green), deletions (red), and unchanged lines (gray). Our Text Diff Checker is essential for code review, document version tracking, configuration comparison, and any scenario where you need to understand exactly what changed between two versions. The comparison runs with a 300ms debounce for smooth real-time updates.

What Is Text Diff Checker?

A diff is the result of comparing two texts and identifying which lines were added, removed, or left unchanged. The classic algorithm computes the longest common subsequence (LCS) of lines between the two inputs: lines in the first text that are not in the LCS are treated as deletions, and lines in the second text that are not in the LCS are treated as additions. The remaining matched lines are unchanged context. This line-by-line approach is what tools like Git use to show changes, and it works well for source code and structured text. For prose, a word-level or character-level diff can be more readable, but line-level diff is the universal default because it is fast and matches how version-control systems represent changes. The output is typically color-coded — green for additions, red for deletions — so a reviewer can see the shape of a change at a glance.

How to Use

  1. Paste the original text in the left textarea.
  2. Paste the modified text in the right textarea.
  3. The diff comparison updates automatically as you type (or click 'Compare Now').
  4. Green lines with '+' prefix indicate additions. Red lines with '-' prefix indicate deletions.
  5. View the summary: total lines added and removed. Copy either original or modified text with the Copy buttons.

Common Use Cases

  • Reviewing changes between two versions of a config file or document
  • Comparing API request or response bodies when debugging integration issues
  • Checking edits made by collaborators before accepting them
  • Verifying that a migration or find-and-replace produced the expected changes
  • Spotting accidental edits when comparing a backup to the current file

Tips & Best Practices

  • The side-by-side layout makes it easy to spot differences at a glance.
  • Line numbers help reference specific changes in code reviews or document discussions.
  • The diff algorithm works on a line-by-line basis — the entire line is marked if any character differs.
  • Use the 'Compare Now' button for a manual refresh when comparing long documents.

Frequently Asked Questions

How is the diff computed?

The tool compares the two inputs line by line using a longest-common-subsequence algorithm, the same family of approach Git uses. Lines present in the original but not in the common sequence are deletions; lines present in the modified text but not in the common sequence are additions.

Can I compare word-by-word instead of line-by-line?

This tool works at the line level, which matches how version control represents changes. For word-level comparison, place each word on its own line before comparing, or use a dedicated prose-diff tool.

Is my text sent to a server?

No. The comparison runs entirely in your browser, so it is safe to paste source code, contracts, or any confidential content. Nothing is uploaded or stored.

Why is a whole line marked when only one character changed?

Line-level diff treats each line as an atomic unit, so any change within a line — even a single character — marks the whole line. This keeps the algorithm fast and the output aligned with how Git displays changes.

This text diff checker runs entirely in your browser. No data is uploaded to any server. Your privacy is completely protected.

Related Tools

Regex Tester

Test regular expressions against text with real-time matching. See matches, groups, and replacements.

JSON Formatter

Format, validate, and beautify JSON data instantly. Parse and fix malformed JSON with syntax highlighting.

Markdown Previewer

Write and preview Markdown in real-time. See how your Markdown renders as HTML instantly.

Text Deduplicator

Remove duplicate lines from text. Sort alphabetically, keep first occurrence, or remove all duplicates.