Diffchecker charges for diff beyond a few comparisons. JSONDiff is covered in ads. Most free JSON tools only format — they don't compare.
The JSON Formatter at Ultimate Tools added a free JSON Diff mode — paste JSON A and JSON B, see added, removed, and unchanged lines highlighted instantly. No account. No paywall.
How to Diff Two JSON Objects
- Open the JSON Formatter & Diff tool
- Click the JSON Diff tab
- Paste your first JSON into the JSON A panel (left)
- Paste your second JSON into the JSON B panel (right)
- The diff appears automatically — no button to press
Green lines with + = added in B. Red lines with − = removed from B. Unchanged lines shown normally. A summary bar counts added, removed, and equal lines.
How the Diff Works
Both JSON inputs are parsed and normalized to 2-space indent before comparison. This eliminates false diffs from formatting differences — if both objects are semantically identical but formatted differently, the diff shows "identical."
The comparison uses the LCS (Longest Common Subsequence) algorithm — the same method used by git diff. It finds the minimal set of changes between the two normalized JSON strings.
Use Cases
API response versioning — Paste the response from two API versions side-by-side. See exactly which fields were added, removed, or renamed between v1 and v2.
Config file auditing — Compare a production config against a staging config. Catch differences before a deployment causes a mismatch.
Code review — JSON payloads in PR descriptions are hard to scan. Paste both versions into the diff tool and share the change summary in the review comment.
Debugging — Two similar JSON objects producing different results in your app? Diff them to find the exact field that differs.
Mock data validation — Compare a mock API response against the real one to catch any fields your mock is missing or has wrong.
Compared to Paid Tools
| Tool | Free diff | Price |
|---|---|---|
| Diffchecker | Limited | $9/month Pro |
| JSONDiff | Yes (ads-heavy) | Free |
| VS Code diff | Yes (local files) | Free (app required) |
| Ultimate Tools | Yes — unlimited | Free |
Formatter Mode Still Works
The JSON Diff tab is an addition — the original formatter is unchanged. Switch to Formatter mode to pretty-print JSON with 2 or 4-space indent, validate syntax in real time, minify in one click, and copy to clipboard.
Related Tools
- generate SHA-256 MD5 file hash online free — verify two JSON files are byte-for-byte identical by comparing their hashes before running a line diff — supports text input and file drag-and-drop
- URL encode decode JSON strings online free — decode percent-encoded JSON embedded in a URL or query parameter before pasting it into the diff panels
- count characters and lines in text free — paste a JSON payload to check its character count and line count — useful for verifying it stays within API size limits before comparing
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