Diff Checker: How to Compare Text Files and Code Online

What is a Diff?

A diff (from "difference") shows exactly what changed between two versions of a text file. Originally a Unix command-line tool, the concept is now central to version control (git diff), code review (GitHub pull requests), and document comparison. A diff shows:

• Lines that were added (typically shown in green)
• Lines that were removed (typically shown in red)
• Lines that were unchanged (context around the changes)

Types of Diff Formats

Side-by-side (split view): The two versions are shown in parallel columns. Changes are highlighted in corresponding lines. Best for reviewing moderate-length files where you want to see context easily.

Unified (inline) diff: The traditional format used by Git. Lines prefixed with + are additions, - are deletions. A header shows the chunk position: @@ -10,7 +10,8 @@ means starting at line 10 of the old file (7 lines) and line 10 of the new file (8 lines).

Common Uses for a Diff Checker

• Code review — comparing a modified function with its previous version before committing
• Configuration changes — spot changes between two versions of a server config file
• Contract/document changes — identify edits between draft versions
• API response comparison — check what changed between two API responses
• Database schema migration — compare schema before and after a migration
• Translation review — compare original and translated text

How the Myers Diff Algorithm Works

Most diff tools use the Myers algorithm (1986), which finds the shortest edit script — the minimum number of insertions and deletions needed to transform one text into another. It's the same algorithm that powers git diff.

Word-Level vs Line-Level Diff

Standard diffs compare line by line. For prose documents or single-line changes, a word-level diff is more useful — it highlights exactly which words changed within a modified line, rather than showing the whole line as changed.

Using the ToolsPal Diff Checker

1. Paste your original text in the left panel
2. Paste the modified text in the right panel
3. Differences are highlighted instantly — additions in green, deletions in red
4. A summary shows the total number of additions and deletions