Diff Checker

About Diff Checker

What is a diff checker?

A diff checker (or difference checker) compares two versions of a text and shows what changed: which lines were removed, which were added, and which words changed inside a line. Use it to check a config before a deploy or to see what changed in a contract. It also compares two API responses and finds why two lines that look the same differ.

How to compare text

1. Paste the old text in the Original tab and the new text in the Changed tab. To open a file, click File or drop the file on the editor. It goes to the tab that is open.
2. The Changes view shows both texts side by side as you type. The icon in the Result header switches to one column (unified). Runs of lines that are the same fold to three lines of context; click a fold to open it.
3. Summary gives the counts and how much of the text is the same. Notes name hidden characters and data changes next to their lines. Patch gives a unified diff to copy or download.
4. Swap (Alt S) changes the places of the two texts.

JSON diff: compare the data, not the lines

A plain text diff marks every line of a JSON file that was minified or had its keys moved, even when the data is the same. Set Compare as to JSON or YAML, or leave it on Auto, and the tool parses both sides, sorts the keys and compares the data. Each change shows by its path. A syntax error stops the compare. The tool marks it in its tab and tells you how to fix it. To check one file on its own, use the JSON Validator or the YAML Formatter.

Options

Open Options to ignore case, whitespace changes, blank lines or line ends. An option that is on shows in the Result header, so you never forget why two different texts count as the same. The tool remembers your choices.

Common surprises

A line that looks the same

A no-break space (U+00A0) often comes from Word, a web page or a PDF. It looks like a space, but a program sees another character, so a config key or a password does not match. The Changes view draws it as NBSP and the Notes name the column.

Price: 10 EUR

Price:[NBSP]10 EUR   (a no-break space after the colon)

Every line changed

When every line shows as changed, the two files often use other line ends: Windows writes CRLF and macOS and Linux write LF. This tool does not mark each line for that. It says once, in the Notes and the Summary, which line ends each side uses. To make them the same, change the setting in your editor or in git (core.autocrlf).

JSON that only moved

Two JSON files with the same data in another order are the same data. Compared as JSON, the result says so.

{ "id": 42, "name": "Ada", "active": true }

{ "active": true, "id": 42, "name": "Ada" }

How a text diff works

A diff looks for the longest list of lines that both texts share in the same order, with gaps allowed. It marks the rest as removed or added. Most tools, this one too, use the algorithm that Eugene Myers published in 1986, which is fast when the texts are close. Inside a changed line, the tool compares words, and characters when the line only looks the same, so the mark falls on the exact place.

The Patch view writes the changes in the unified diff format that git and code review tools read. Lines that start with - were removed, lines with + were added, and each part starts with a line such as @@ -3,7 +3,8 @@.

--- original.txt
+++ changed.txt
@@ -1,3 +1,3 @@
 Refund policy
 
-You can return any item within 14 days of delivery.
+You can return any item within 30 days of delivery.