Word File Compare - Online Diff for Two Word Documents
Upload two .docx files to extract and compare their text side by side: additions highlighted green, deletions marked red, inline word-level changes, plus an overall similarity score. Everything runs locally in your browser — no file ever leaves your device.
How to compare two Word files
The page opens in "Upload Word" mode: drag the original document into the left drop zone (or click to choose a file), then drop the revised document on the right — comparison starts automatically once both files are parsed. You can also switch to "Paste Text" mode to compare two blocks of text directly. Results appear in two aligned panes: the original on the left, the revision on the right. Added lines are green in the right pane, deleted lines are red in the left pane, and modified lines highlight the exact changed words inline. The stats bar shows the similarity percentage and added / removed / modified / unchanged line counts, and "Copy Result" exports plain text with +/- prefixes for email or tickets. For plain-text comparison use the Text Diff tool; after comparing, batch edits are easy with the Text Replace tool.
About this Word comparison tool
Everything is computed locally in your browser: .docx files are read via FileReader and parsed with the mammoth library to extract body text, then aligned and highlighted with jsdiff's Myers diff algorithm, and finally scored with the difflib formula (2 × matched characters ÷ total characters of both sides). Files are never uploaded, so comparison even works offline — safe for contracts, bids and other sensitive documents. Before comparing, text is normalized automatically: line endings unified (CRLF→LF), trailing whitespace trimmed, consecutive blank lines collapsed and BOM stripped, so formatting noise never produces a screen full of false positives. Known limits: .docx only; body text is extracted, so tables are flattened and footnotes, comments and text boxes may be lost; beyond 3,000 lines or 150,000 characters per side only the first portion is compared with a notice; over-long lines or an exhausted inline budget degrade to whole-line highlighting without word-level detail.
Common use cases
Contract review: compare a client-returned revised contract against the original side by side to spot clause additions, deletions and amount changes at a glance. Thesis revision: check every edit against your supervisor's marked-up version, and paste the copied diff into your response letter. Bids and proposals: after merging multiple rounds of a bid document, verify the final version carries no leftover content from earlier drafts. Policy and SOP updates: generate an old-vs-new difference summary to send company-wide without manual proofreading. Lists and configs: switch to the "Paste Text" tab to compare checklists, configuration blocks or code snippets with the same precision.
Legend and metrics explained
Color legend: green in the right pane = added content; red in the left pane = deleted content; both panes colored = the line was modified, with dark inline fragments marking the exact changed words. Similarity: calculated as 2 × matched characters ÷ total characters of both sides; 100% means identical. Results are floored, so 99.9% never rounds up to 100%. Line counts: added / removed / modified are counted per line, "unchanged" counts identical lines; each line number is the original line number in its own document for easy lookup. Copied result: exported plain text prefixes additions with "+ ", deletions with "- ", and outputs both lines for every modification.
Frequently Asked Questions
Is the .doc format supported?
No. .doc is the binary format of Office 2003 and earlier; this tool only supports .docx. Open the file in Word / WPS and use "Save As" to choose the .docx format, then upload again. If you only have a .doc file, switch to the "Paste Text" tab and paste the body text for comparison instead.
Are my files uploaded to a server?
No. .docx files are read and parsed locally in your browser — no data is ever sent to a server, and comparison works offline, making it suitable for sensitive documents such as contracts, bids and theses.
What content of the document is compared?
The tool extracts the body text for comparison: tables are flattened into line-based text, images are not compared, and footnotes, comments and text boxes may be lost. Formatting such as fonts, sizes and colors does not affect the result — only the text itself is compared.
How is the similarity percentage calculated?
Using the difflib formula: similarity = 2 × matched characters ÷ total characters of both sides. Identical documents score 100%, completely unrelated ones close to 0%. Changing a single word in one line usually keeps similarity above 95%. Results are floored to one decimal, so a real difference never shows as 100%.
Why does a moved paragraph show as one deletion plus one addition?
Consistent with git diff and every mainstream diff tool, content moves are rendered as "delete + add" rather than being recognized as a move. When a paragraph moves from page 3 to page 5, you will see it marked red (deleted) in the left pane and green (added) in the right pane — the paragraph text itself is unchanged.
Are there file-size or line-count limits?
Each file may be up to 50MB; above 30MB the tool suggests using a smaller file instead (parsing takes a few seconds and may stall on phones). If one side exceeds 3,000 lines or 150,000 characters, only the first portion is compared and a truncation notice appears above the result. For longer documents, split them by chapter and compare in passes, or use the "Paste Text" tab.
Why do some modified lines lack inline highlighting?
When a single line exceeds 400 characters, or the inline-highlight budget (40,000 characters) is exhausted, that line degrades to whole-line highlighting — you can still see which line changed, just not down to the word. This is a deliberate degradation to keep very large documents from freezing the browser; normal documents never trigger it.
How is this different from the Text Diff tool?
The Text Diff tool requires manually pasting two blocks of text and suits code, configs and checklists; this tool reads .docx files directly and extracts the body text, making it ideal for comparing Word document versions. This page also offers a "Paste Text" tab for pasted content — see theText Diff tool
Can I copy or share the comparison result?
Click "Copy Result" to get plain text with prefixes: lines starting with "+ " are additions, "- " are deletions, and a modified line outputs both its deletion and addition lines. Paste it straight into email, tickets or chat. Since files never leave your browser, sharing the copied text never exposes the original document.