Online Diff Checker: Compare Two Texts, Files or Code Side by Side
Spotting differences between two versions of text, code, or documents is tedious when done manually. A diff checker highlights every change — additions, deletions, and modifications — at both line and character level, making comparison instant and error-free.
Try Diff Checker Free →What Diff Checking Does
A diff tool compares two text inputs and highlights the differences: green for added lines/characters, red for removed lines/characters, and yellow/blue for modifications. The result shows both a summary of changes and the full annotated comparison.
Line-by-Line vs Character-Level Diff
Line diff shows which lines changed. Character diff shows the exact characters that changed within a line. For code, line diff is usually sufficient. For prose text where small word changes matter (legal contracts, edited documents), character-level diff is more useful.
Use Cases for Diff Checking
Code version comparison (before/after a refactor). Reviewing contract revisions (see exactly which clauses changed). Comparing API responses to debug behavioral changes. Reviewing edited documents or articles. Checking configuration file changes between environments.
Diff Algorithms Explained
Formly uses the Myers diff algorithm — the same algorithm used by Git. It finds the shortest edit script: the minimum number of insertions and deletions needed to transform text A into text B. This ensures the most natural-looking diff that matches human intuition about what changed.
Comparing Code Files
For code comparison, the diff checker preserves indentation and handles whitespace-only changes separately. You can toggle "ignore whitespace" to see only meaningful code changes, or include whitespace to see formatting differences.
Document Version Control
Non-technical users use diff checkers to track document revisions: legal agreements, business proposals, academic papers. The visual format of the diff is much clearer than Microsoft Word's "Track Changes" for understanding what changed between versions.
Frequently Asked Questions
Is there a text length limit?⌄
Each input supports up to 50,000 characters. For larger files, split into sections.
Can I compare files?⌄
Upload two text files and the diff checker compares their contents. Supports .txt, .js, .py, .json, .csv, and other text-based formats.
Does it work for code comparison?⌄
Yes. The diff checker handles code with proper syntax-aware comparison and whitespace options.
Is it free?⌄
Yes. Completely free with no limits.
Can I share the diff result?⌄
The page state is saved in the URL, so you can bookmark or share a link to a specific comparison.
Try Diff Checker — It's Free
No signup needed. 5 free uses daily. Pro plan from $9.99/month.
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