API Diff Checker — Response Comparison Tool
Compare two API response payloads and highlight added, removed, and changed fields. Paste any two JSON responses to get an instant field-level diff with color-coded changes and a summary count.
How to Use API Diff Checker — Response Comparison Tool
How to Use the API Response Diff Checker:
Load a Preset: Click any of the preset buttons to instantly load a real-world example — API version changes, order status transitions, or deployment config diffs. Presets are the fastest way to understand the tool before pasting your own responses.
Paste Response A: In the left textarea, paste the baseline JSON response — typically the older version, the "before" state, or the first API version. The field is labeled "Response A — baseline / before." The comparison always treats A as the reference point.
Paste Response B: In the right textarea, paste the updated JSON response — the newer version, the "after" state, or the second API version. The diff will show what changed between A and B.
Review the Live Diff: The diff updates automatically as you type. No button click needed. The results appear below the inputs with color-coded rows: green for added fields, red for removed fields, amber for modified fields, and gray for unchanged fields.
Read the Summary Badges: The four colored badge buttons below the action bar show the count for each change type (Modified, Added, Removed, Unchanged). Click a badge to filter the diff table to show only that type of change. Click again to clear the filter.
Toggle Unchanged Fields: By default, unchanged fields are hidden to keep the diff focused on what changed. Check the "Show unchanged" checkbox to include all fields in the results, which helps verify that specific fields were intentionally preserved.
Use the Action Bar: Four action buttons are available: Swap A ↔ B (reverse the comparison direction), Format JSON (pretty-print both inputs for readability), Copy Diff (copy the changes as a unified +/-/~ text format), and Clear (reset both inputs).
Read Modified Field Rows: For modified fields, the diff shows the old value with a strikethrough in red, and the new value in green directly below — making it easy to see exactly what value changed without switching between tabs.
Common Use Cases:
- API versioning: Compare v1 and v2 endpoint responses to understand breaking changes before migrating clients.
- Before/after testing: Verify that a code change or bug fix only modified the expected fields.
- Deployment validation: Confirm that a production deploy changed only the intended config or data fields.
- Contract testing: Check that an API response still matches a documented schema after refactoring.
- Debugging regressions: Paste two recorded API responses to find exactly which field value diverged.
- Integration review: Share a diff summary with teammates to communicate what an API change affects.
- Data pipeline auditing: Compare transformed output before and after a pipeline change.
Tips and Best Practices:
- Use the Format JSON button to pretty-print minified responses before comparing — it makes the input easier to read and paste corrections.
- The diff compares leaf-level scalar values (strings, numbers, booleans, null) by path, so nested object changes are shown at the deepest modified field, not at the object level.
- Arrays are treated as atomic values — if an array changes, the entire array path is marked as modified, not individual array elements.
- The Copy Diff output uses +/−/~ prefixes compatible with many diff viewers and can be pasted directly into GitHub comments or Slack messages.
- Click the type filter badges to focus on just the changes that matter — e.g., click "Added" to see only new fields introduced in Response B.
Frequently Asked Questions
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