How to Compare Two Text Files Online (Free)
Whether you're reviewing config file changes, comparing two API responses, checking contract revisions, or reviewing code without a git setup, a diff tool shows you exactly what changed — in seconds. This guide shows you how to use the browser-based Diff Checker to compare any two texts without installing anything.
Step-by-Step Instructions
Open the Diff Checker
Go to the Diff Checker tool. Two side-by-side panels are shown: original (left) and revised (right).
Paste the original text
Click the left panel and paste the original version of your text. This might be the old config file, the baseline document, or the first draft.
Paste the revised text
Click the right panel and paste the new or changed version. This might be the updated config, the edited document, or the second draft.
Click Check Diff
Press the Check Diff button. The tool uses a Myers diff algorithm (the same algorithm used in GNU diff and git diff) to find the minimal set of changes between the two texts.
Read the color-coded output
Green lines (prefixed with +) are lines that exist in the revised text but not the original — they were added. Red lines (prefixed with −) exist in the original but not the revised — they were removed. Lines with no prefix are unchanged.
Read the summary
Below the diff, a summary shows the number of added and removed lines. This is useful for quickly gauging how large the change was before reading the details.
Common Use Cases
- Config file review: Compare nginx.conf or docker-compose.yml before and after an update to verify only the expected lines changed.
- API response debugging: Paste two JSON responses side by side to find which field changed between requests.
- Document editing: Compare two drafts of a contract, specification, or README to review what the editor changed.
- Clipboard compare: When you have two text snippets in your clipboard history and want to spot the difference quickly.
Is My Data Private?
The diff runs entirely in your browser using a vanilla JavaScript implementation of the Myers diff algorithm. Both text panels are processed locally — no data is sent to a server. Sensitive config files, credentials, and proprietary documents stay in your browser tab only.