Diff Checker
Find what changed between two texts.
How to use Diff Checker
Compare two blocks of text and list the lines that appear only on the left or only on the right.
Open Diff Checker on toolpermarket — the form is ready, so type your numbers and read the result.
In the Original field, paste the first or older version of the text. Order matters only for the direction of added or removed lines.
In the Changed field, paste the second or newer version to compare against. Use line mode for code and word mode for prose.
Press Compare to compute the result. The output appears immediately below the form. Edit a value and press the button once more to see the updated answer.
Read the result and use it as needed. If the number looks off, re-check your inputs and run it again — the math is deterministic, so the same entries always return the same answer.
Worked example. Comparing a draft with one edited line highlights that single changed line in green while everything else stays neutral.
Tips for accurate results.
Switch to word-level diff for paragraphs, line-level for code.
Ignore whitespace when only indentation shifted.
Copy the result into a review comment to show exactly what changed.
When to use Diff Checker. Reviewing a teammate's edit before merging. Spotting what changed between two config versions. Showing a reviewer the precise delta, not the whole file.
When you actually reach for this
- You changed a config or a block of code and need to see exactly which lines differ between two versions.
- You are reviewing a teammate's paste and want a line-by-line comparison instead of eyeballing it.
Where this tool stops being accurate
- Line-based diffs miss within-line edits; a whole line shows as replaced even if one word changed.
- Whitespace-only changes can dominate the view unless you ignore blanks, which can hide meaningful indentation fixes.
Frequently asked questions
What is the difference between line and word diff?
Line diff compares whole lines and is ideal for code or lists, flagging an entire changed line even if only one word moved. Word diff goes finer, highlighting just the substituted words inside a paragraph, which reads better for prose. Pick the mode that matches the granularity you actually care about.
Why do whitespace-only changes show up?
By default a diff treats re-indentation as a real change because the bytes differ. Most diff tools, including this one, offer an ignore-whitespace option that collapses pure spacing edits so you can focus on meaningful content changes between versions.
Is the comparison stored anywhere?
No. Both texts are compared locally on your device and nothing is uploaded or saved. You can close the tab afterwards with confidence that the contents of either version were not transmitted to a server.
My one-character edit shows the entire line as changed — normal?
Yes, line diffs replace the whole line. Enable character-level or word-level highlighting if you need to see the exact edit.
Why do trailing spaces show as differences?
They are real characters to a diff. Turn on "ignore whitespace" if those changes are noise, but be careful it does not hide an intentional indent fix.