Compare any two pieces of text and see exactly what changed. Words added, words removed, and everything that stayed the same – all highlighted clearly in one view.
This tool works well for writers, developers, students, and marketers. It is especially useful when you want to compare your original content with an AI-rewritten version to see what the AI actually changed.
Paste your original and revised text in the boxes below, choose word-level or character-level mode, and click Compare.
Compare & Analyze Your Text
Paste your original text and revised text below, then click Compare to instantly highlight every addition, deletion, and unchanged word. Perfect for comparing original content vs AI-rewritten versions — see exactly what changed, what was kept, and how similar the two texts really are.
What This Tool Does
The Text Difference Checker is a free diff checker online that compares two versions of any text at the word level or character level. It highlights additions in green and removals in red with strikethrough, so you can read through changes quickly without guessing.
It also shows a stats panel with word counts and a similarity percentage, so you know at a glance how much the two texts differ. Everything runs in your browser. No data is sent anywhere.
This is built on the LCS (Longest Common Subsequence) algorithm, the same method used in tools like Git to track code changes. It gives accurate, line-by-line results rather than rough estimates.
If you use AI writing tools regularly, our AI Prompt Generator can help you write better prompts to get more consistent output from models like ChatGPT or Claude. And if you want ready-made prompts for content writing, editing, and more, browse the AI Prompt Library.
Features
- Word-level diff and character-level diff with a one-click toggle
- Added text highlighted in green, removed text in red with strikethrough
- Unchanged text shown in normal color for easy reading
- Stats panel showing words added, words removed, words unchanged, total word counts for both texts, and similarity percentage
- Clear All button to reset both fields instantly
- Copy Result button to copy the diff output to your clipboard
- Works fully in your browser with no login or account needed
- Responsive layout that works on mobile and desktop
How to Use the Text Difference Checker
Step 1. Paste your original text into the left box labeled “Original Text.”
Step 2. Paste your revised or edited text into the right box labeled “Revised Text.”
Step 3. Choose your diff mode. Select “Word-level” to compare whole words, or “Character-level” to compare every single character.
Step 4. Click the Compare button. The diff result appears below with color-coded highlights.
Step 5. Read through the stats panel to see how many words were added, removed, or kept the same, and what the similarity percentage is.
Step 6. Use the Copy Result button to copy the highlighted output, or click Clear All to start fresh.
You can also press Ctrl + Enter inside either text box to trigger the comparison quickly.
Who Uses This Tool
Content writers and editors use it to review edits made to their drafts. Instead of reading both versions separately, they can see every change in one place.
People using AI writing tools use it to compare their original writing with AI-generated rewrites. This makes it easy to see which sentences the AI changed and which it kept.
Students and academics use it to check the difference between two versions of an essay or report before submitting a final draft.
Developers and technical writers use it to compare documentation versions, changelogs, or any plain-text files where tracking changes matters.
Translators and proofreaders use it to compare source text with revised translations or proofread versions to catch missed changes.
Frequently Asked Questions
What is a text difference checker?
A text difference checker is a tool that compares two pieces of text and shows what is different between them. It marks additions, deletions, and unchanged parts so you can see changes clearly without reading both texts line by line.
What does “diff” mean in a diff checker online?
The word “diff” comes from diff, a Unix command-line tool created in the 1970s to compare files. Today it refers broadly to the process of finding differences between two text inputs. An online diff checker does the same thing in a browser without any software installation.
Is this diff online checker free to use?
Yes. The tool is completely free. There is no account, no login, and no usage limit. It runs entirely in your browser.
What is the difference between word-level and character-level diff?
Word-level diff compares your texts word by word. Character-level diff compares every individual character. Word-level is better for reading content changes. Character-level is better for spotting small edits like punctuation changes, spacing, or single-character typos.
How is the similarity percentage calculated?
The similarity score is based on the proportion of matching tokens between the two texts. A score of 100% means the texts are identical. A lower score means more of the content was changed.
Can I use this to check if AI rewrote my content too much?
Yes. Paste your original writing in the left box and the AI output in the right box. The tool shows you exactly which words were kept and which were replaced, so you can judge whether the AI version matches your intent.
Does this tool store my text?
No. All processing happens in your browser using JavaScript. Nothing is sent to any server. Your text stays on your device.
What is the longest text I can compare?
There is no hard character limit. For very large texts (several thousand words), the comparison may take a second or two since it runs client-side. For most practical use cases it is instant.
Can I use this on my phone?
Yes. The tool is fully responsive and works on mobile browsers without any issues.
Is this the same as a plagiarism checker?
No. A plagiarism checker compares your text against external sources on the internet. This tool only compares the two texts you paste into it. It does not check anything online.