Try the free tool below. It runs in your browser, with no sign-up and no download.
What Is the JSON Diff Checker?
JSON is the format most apps use to exchange data, and small changes in a JSON file can change how an app behaves. Our JSON diff checker compares two JSON texts side by side and highlights exactly what was added and what was removed. Added parts show in green, removed parts show in red, and unchanged parts stay plain.
The comparison uses the diff library in your browser, line by line or word by word, and it counts how many characters were added, removed, or left unchanged. Your texts never leave your device, which is important when JSON holds API responses, user data, or internal settings.
How to Use It
Paste the first JSON text on the left and the second on the right, then press Compare. The result shows the full text with changes marked, so you can read the difference in context instead of guessing from a short summary. Switch between line mode and word mode: line mode is best for spotting moved or added lines, while word mode is best for small value changes inside one line.
Press the sample button to see a worked example. In the sample, one value changes from 12 to 15 and a new key appears, and both changes are marked clearly.
When Is It Useful?
Use it when an API starts returning different data and you need to find what changed. Use it when a settings file was edited by someone else and you want to review the edit. Use it when a test fails because the expected output and the real output differ, and the difference is hard to see by eye.
It is also useful for code review. Pasting the old and new versions of a small JSON payload into the checker gives a reviewer a clear view of the change without opening a heavy tool.
Tips for Clear Diffs
For the clearest result, format both JSON texts in the same style before you compare them, with the same indent and key order. That way the checker marks real content changes, not spacing noise. If your JSON is not formatted, paste it into a formatter first, then compare the two formatted versions.
When a file is large, compare one section at a time. A focused diff is easier to read than a huge one, and it helps you fix the exact change that matters.
Frequently Asked Questions
Is my JSON sent to a server? No. The comparison runs in your browser.
Does it check that my JSON is valid? The checker compares text. If a text is not valid JSON, compare it as plain text or fix it first with a JSON formatter.
What is the difference between line and word mode? Line mode marks whole changed lines. Word mode marks only the changed words inside a line.
Can I compare files? Copy the file contents into the two boxes. The tool works on pasted text.
A Worked Example: Chasing an API Change
Suppose your app worked yesterday and fails today, and you suspect the API changed its response. Save a copy of yesterday’s response and today’s response, paste them into the two boxes, and compare by lines. The diff marks the changed lines at once: perhaps a field renamed from user_name to username, or a number that used to be a string and is now a real number. That single renamed field is often the whole bug, and the diff shows it in seconds, while reading both responses by eye could take many minutes. Switch to word mode to confirm the exact characters that changed inside a long line, such as a URL with one different segment. Then fix your code to match the new field, or ask the API owner whether the change was planned. Keeping a small folder of saved responses, one per release, makes this check repeatable, and it turns a stressful outage into a short, methodical task. The habit of diffing before guessing saves time on almost every data problem.
When you report the change to a teammate, paste the marked diff into your message. A visible diff explains the problem faster than a paragraph describing it, and it leaves a clear record of what changed and when.
Also in Spanish
This tool is also available in Spanish: Comparar dos JSON Online Gratis – Encuentra Diferencias al Instante.