Text Diff Viewer

What a line marker means

Each side is split on \n only. A carriage return stays on the line, so a Windows row that still contains \r will not match the same letters without \r. The longer side decides how many rows exist. A missing row on the short side is the empty string, not a skipped comparison. When both strings at that index are equal, the row is two spaces plus the text. When they differ, the block emits a minus, a space, and the original line, then a newline, then a plus, a space, and the updated line.

The sample a / b / c against a / c is the cascade. Row 1 is two spaces and a. Row 2 is minus b and plus c. Row 3 is minus c and plus, then a space, because the updated side has no third line. A reader who expected the tool to notice that c only moved down will not see a single deletion of b. The page never computes a longest-common-subsequence alignment. Equal lines stay matched only while they share an index.

Presets and the record button

Compare preset lists Custom, API response drift, Environment config, and Copy editing. Choosing a named preset replaces both panes and sets the menu to that preset. API response drift puts {"status":"ok","count":2} on the left and {"status":"ok","count":3,"page":1} on the right, each as one line, so the diff is a single minus row and a single plus row. It does not parse JSON. Environment config is two KEY=value lines on each side. Copy editing is Fast setup / Zero config / Quick start against Fast setup / Zero configuration / Instant start. The first of those three rows matches. The other two are replacements at the same indexes.

Typing in either pane sets the menu back to Custom and keeps what you typed. It does not restore the text from before the preset. The page stores a short list of preset keys you picked, but it never shows that list, so there is no history menu to reopen an older custom draft. Record diff action leaves Line diff untouched. If the block looks wrong, the panes are the cause, not a missed click on that button. Copy output copies the block that is already visible, including the two-space prefix on unchanged rows.

Jobs for a positional reading

Use the panes when a line's position is the identity: env files with the same keys in the same order, a stanza you edited in place, or the Copy editing preset. The markers are easy to scan because a change is always a pair of rows and a match is always an indented row. JSON with added keys is a poor fit when you care about the key rather than the character line. The JSON compare tool walks property paths. The API preset on this page is only two strings, so a new key looks like the whole line was replaced.

Rewriting text, rather than viewing it, is Find & Replace. Joining or splitting lines before you compare them is line operations. This viewer will not ignore whitespace, will not hide unchanged rows, and will not diff inside a line at word level. Zero config against Zero configuration is one full-line replacement even though the words share a prefix.

Blank rows, a fresh visit, and saved panes

Two empty panes are one empty row compared with one empty row. They count as equal, so Line diff is two spaces and nothing else. That value is published after the page hydrates, and Copy output will copy those two spaces. A blank line in the middle of both panes is the same two-space row. A blank line on only one side is a minus or plus row whose text is empty, which still includes the sign and the following space.

Both panes, the selected preset name, and the unshown preset-key list are written to local storage for this browser and restored on the next visit. A reload brings the last pair back. It does not offer a button to forget them. Clearing the browser's site data does. The record button is not a save action. The save already happened when the panes changed.

Rules and limitations

Lines are paired by index after a split on newline. Carriage returns stay. Equal rows are two spaces plus the text. Unequal rows are a minus row and a plus row. A missing side is the empty string.

Presets replace both panes. Editing returns the menu to Custom without an undo stack. Record diff action does not change the diff. Panes are restored from local storage. There is no download and no word-level compare.

Common problems

If every line after an insertion looks changed, the compare is positional. A new row pushes the later rows onto new indexes. This page will not realign them.

If Record diff action seemed to do nothing to the text, that is what it does. The block you are looking at is already the result.

Frequently asked questions

About this tool

Maintained by Toolbench. For large or deeply nested files, split the input into smaller batches and verify representative results before using them in an import or application. Report reproducible problems through Contact.