Diff Checker — Compare Two Texts Side by Side
Find every added, removed and changed line between two blocks of text.
🔒 Runs in your browser — files never uploaded ⚡ No signup 💯 Free
This tool needs a wider screen
Comparing two texts side by side needs room for both panes at once. On a phone the columns become too narrow to read, so this one is desktop and tablet only.
Paste two versions of anything — a config file, a contract, a block of code, a draft — and see exactly what changed between them. Lines are matched with a longest-common-subsequence diff, the same approach behind git diff, so unchanged blocks stay aligned instead of drifting out of sync after a single inserted line.
Everything runs in your browser. Nothing is uploaded, which matters when the text you are comparing is a production config or an unsigned agreement.
How to use Diff Checker
- Paste the original into the left pane.
- Paste the changed version into the right pane.
- Click Compare — or press Ctrl+Enter from either pane.
- Read the result. Green is added, red is removed, amber is a modified line. The counters above the output summarise the whole comparison.
Reading the output
Line numbers on each side let you jump straight to the change in your own editor. Where a line was replaced rather than purely added or deleted, the two versions are paired on the same row and marked amber, so you can read the before and after together.
Ignore trailing whitespace is on by default — it suppresses the noise from editors that strip or add spaces at line ends. Turn it off when whitespace is significant, as in Markdown line breaks or YAML.
Why this tool is desktop only
Two readable text columns need roughly 900 pixels. Below that the panes get so narrow that lines wrap constantly and the alignment that makes a diff readable falls apart. Rather than ship a version that technically loads but is useless, we show this tool only where it works properly. The rest of this page — the explanation, the FAQ, the related tools — is available on any device.
Frequently asked questions
Is my text uploaded anywhere?
No. The comparison runs entirely in your browser using JavaScript. Nothing is sent over the network, which is why this is safe for config files, contracts and unreleased code.
Why can't I use this on my phone?
A side-by-side diff needs two readable columns, which takes about 900 pixels of width. On a narrower screen the panes wrap so aggressively that the alignment stops being readable. Open this page on a tablet or desktop and the tool appears automatically.
How large a file can I compare?
Up to 3,000 lines per side. The diff algorithm builds a comparison table proportional to the two lengths multiplied together, so beyond that your browser starts to struggle. For larger files use git diff or a desktop diff tool.
Does it compare word by word within a line?
Not currently — comparison is line by line, and a changed line is shown in full on both sides. Word-level highlighting inside modified lines is on the roadmap.