Diff Checker
Compare two versions of any text, config, log or code and see exactly what changed. Paste an original and a changed version, press Compare, and every line is marked added, removed or unchanged — with the exact words that changed highlighted inline. Toggle ignore whitespace or ignore case to filter out cosmetic noise. Everything runs in your browser; nothing is uploaded.
The comparison runs entirely in your browser — nothing is uploaded. Safe for diffing a production config, a firewall ruleset, a log excerpt or a policy document without it ever leaving your machine.
What this tool is
- A free, in-browser diff checker: paste an original and a changed version of any text, and see every line marked added (green), removed (red) or unchanged.
- Computes a true line-level diff with a longest-common-subsequence (LCS) algorithm, then highlights the exact words that changed inside a replaced line.
- Toggle “ignore whitespace” to skip indentation and trailing-space noise, and “ignore case” to treat differently-cased text as equal.
- Get an at-a-glance add / remove / unchanged count and copy the result as a unified +/- diff.
- Everything runs client-side in your browser — nothing you paste is ever sent to a server, so it is safe for configs, logs and policy documents.
What is a diff?
A diff (short for "difference") is a structured comparison of two versions of some text that shows what was added, what was removed, and what stayed the same. Rather than forcing you to scan two blocks of text side by side and spot the change by eye, a diff aligns the two versions and marks each line, so the one altered rule, flipped value or reworded clause stands out immediately. It is the idea behind the Unix diff command, version-control history, and every code-review screen.
Line, word and character diffs
- Line diff. Each whole line is one unit. Any edit marks the old line removed and the new line added. This is the right default for code, configs and logs, where changes are line-oriented.
- Word diff. Compares word by word. Better for prose — it shows that only a phrase inside a sentence changed instead of flagging the entire line. This tool highlights changed words inline within a replaced line.
- Character diff. The finest grain — individual characters. Best for catching a single typo or a changed digit in an otherwise identical line.
How this tool computes the diff
It splits both inputs into lines and finds their longest common subsequence (LCS) — the longest ordered set of lines the two versions share. Everything in the original but not in that subsequence is a deletion; everything in the changed version but not in it is an addition. The LCS approach is what makes the result stable and minimal rather than naively marking every line after the first change. Within a line that was replaced, the same algorithm runs again over word tokens to highlight just the words that differ. The ignore whitespace and ignore case options change only how lines are matched — the text shown is always exactly what you pasted.
Where a diff earns its keep
- Config review. Diff a firewall ruleset, nginx/SSH config, IAM policy or Kubernetes manifest before and after a change to confirm only the intended lines moved — and catch a flipped allow/deny, a widened CIDR or a changed port.
- Log triage. Compare two log excerpts to isolate exactly what a deployment or an incident added or stopped emitting.
- Policy & document review. See precisely what a vendor reworded in updated terms, or what a revision changed in a security policy or runbook.
- Code review. Read a patch as what it actually changes, line by line, with the edited words called out.
Privacy note: the comparison is computed entirely in your browser with JavaScript — there is no network request to diff your text and nothing is stored. That makes it safe to paste sensitive material such as production configuration, access-control policy, internal logs or an unpublished document; the content never leaves your machine.
Frequently asked questions
What is a diff, and what does a diff checker do?
A “diff” (short for difference) is a comparison between two versions of text that shows exactly what changed from one to the other. A diff checker takes an original version and a changed version, lines them up, and marks each line as added, removed or unchanged. This tool displays additions in green and deletions in red, keeps the unchanged lines for context, and — inside a line that was edited rather than wholly replaced — highlights the specific words that differ. It is the same idea behind the output of the Unix "diff" command and the side-by-side views in code-review tools, but it runs instantly in your browser on any text you paste.
What is the difference between a line diff, a word diff and a character diff?
They differ in the unit being compared. A line diff treats each whole line as one unit, so any change to a line marks the old line removed and the new line added — this is the standard view for code, config files and logs because changes there are naturally line-oriented. A word diff compares word by word, which is better for prose and shows that only a phrase inside a sentence changed rather than flagging the entire line. A character diff goes finer still, comparing individual characters, which is useful for spotting a single typo or a changed digit. This tool runs a line diff for structure and then applies an inline word-level diff within each replaced line, so you get both the big picture and the precise edit.
What do “ignore whitespace” and “ignore case” do?
Ignore whitespace makes the comparison treat lines that differ only in spacing — indentation, trailing spaces, tabs versus spaces, or collapsed runs of spaces — as equal, so reformatting or re-indentation does not flood the result with false changes. Ignore case treats uppercase and lowercase as the same, so "Error" and "error" are considered identical. Both options only affect how lines are matched; the tool always displays the original text exactly as you pasted it. They are useful when you care about meaningful content changes and want to filter out cosmetic ones.
What is this useful for in security and operations work?
Diffing is a core review habit. Compare a firewall ruleset, nginx or SSH config, IAM policy or Kubernetes manifest before and after a change to confirm that only the intended lines moved. Diff two log excerpts to isolate what a deployment or an incident added. Compare a vendor’s updated terms, a security policy revision, or two versions of a runbook to see precisely what was reworded. In code review it shows what a patch actually does. Because the comparison is line-accurate, it catches the small, dangerous change — a flipped allow/deny, a widened CIDR, a changed port — that is easy to miss when skimming two files side by side.
Is my text uploaded anywhere?
No. The entire comparison — splitting into lines, the LCS line diff, the inline word diff and the rendering — happens locally in your browser using JavaScript. Nothing you paste is sent to PlayCISO or any third party, there is no network request involved in computing the diff, and nothing is stored. That makes it safe to compare sensitive material such as production configuration, access-control policies, internal logs or unpublished documents without the content ever leaving your machine.