A short guide to API Response Diff
Compare changes without losing the signal.
Compare two JSON responses and see structural, type, and value changes. Here is the practical way to prepare the input, read the output, and decide what to check next.
01
When to reach for it
Compares two JSON documents, flattens their paths, and reports added, removed, type, and value changes. It is most useful when you are dealing with response changed or contract drift. Start with the smallest example that still shows the behavior.
- Look for response changed, contract drift, missing field.
- Reduce the example until one observation can change the result.
02
How to prepare the input
Paste a focused example in two JSON responses separated by ---. Leave out unrelated noise so the result stays easy to verify.
- Use the accepted format: two JSON responses separated by ---.
- Keep the facts that make the behavior reproducible.
- Do not treat missing context as a reason to invent an answer.
Example input
Safe sample
{"id":1,"status":"ready","items":[1,2]}
---
{"id":1,"status":"queued","items":[1,2,3],"traceId":"abc"}Run this first to see the shape of the result. Then change one meaningful fact and confirm that the output changes with it.
03
How to read the result
Lists input-derived added, removed, type, and value changes between the two responses. Start with the first structural change, then decide whether it explains the symptom. A larger output is not automatically more important.
- Separate the observed fact from the suggested next check.
- Prefer the smallest reversible experiment that can confirm or reject the finding.
- Save the output when it belongs in an incident note, review, or handoff.
04
Know the boundary
A diff shows what changed; it cannot tell you whether the change was intentional or why it happened.