Text & Code Diff Checker, Side-by-Side View

Comparing two versions of a config file, an API response captured before and after a change, or a code snippet someone edited, by eye, line by line, is slow and genuinely error prone, the human eye is not built to reliably spot a single changed character buried in an otherwise identical paragraph. This tool computes an actual line by line diff between two blocks of text and highlights exactly what was added, removed, and left unchanged, the same underlying approach used by version control systems, without needing a full git setup for a quick one-off comparison.

How a real diff differs from a naive line by line comparison

A naive comparison, simply checking whether line 1 of the original matches line 1 of the changed version, line 2 against line 2, and so on, breaks down the moment a single line is inserted or deleted anywhere in the middle of the text, since every line after that point shifts by one position and appears to mismatch even though nothing about it actually changed. This tool instead computes the longest common subsequence between the two versions, the same algorithmic approach behind tools like diff and git diff, which finds the actual minimal set of additions and removals needed to transform one version into the other, correctly recognizing that most of the surrounding content is identical even when lines have shifted position.

Reading the output

Each line in the result is marked with a plus sign and a green background if it was added in the changed version, a minus sign and a red background if it was removed from the original, or left unmarked with a neutral background if it is identical in both. Line numbers are shown for each side independently, so an added line shows its position in the changed version, and a removed line shows its position in the original, matching the way most code review tools present a diff.

Ignoring whitespace and case when they don't matter

A line that differs only by trailing whitespace, an extra space, or letter casing is often a false positive you don't actually care about, particularly when comparing content that passed through different formatting tools or copy paste sources along the way. The ignore whitespace option normalizes leading, trailing, and repeated internal whitespace before comparing, and the ignore case option compares text case-insensitively, both letting you filter out formatting noise and focus specifically on the substantive content changes that actually matter for your comparison.

Works on any line based text, not just code

While this tool is genuinely useful for comparing source code, it works identically well on any text organized into lines: two versions of a config file, before and after an API response for the same request, two drafts of a document, or a list of values before and after a data cleanup pass. The underlying line diff algorithm has no idea what language or format it is looking at, it simply compares lines of text, which is exactly what makes it flexible enough to handle whatever you paste in.

Runs entirely in your browser

The diff calculation runs directly in your browser using standard JavaScript, nothing you paste into either box is sent to a server, logged, or stored. This makes it safe to compare content containing real, unreleased, or sensitive data, an internal config file, a real API response, without exposing that content to a third party service. If the two versions you are comparing are JSON specifically and you want them formatted consistently before diffing, our JSON Formatter is a useful first step, part of the same Developer Utilities collection this tool belongs to.