API versioning and JSON diff in UK tech
When a UK fintech or government digital service ships a new API version, the first question is: what actually changed between v1 and v2? Pasting both JSON responses here gives an immediate colour-coded answer , green for additions, red for removals, amber for modifications. The GOV.UK API standards mandate backwards-compatible changes wherever possible; this tool makes it easy to verify that a new release honours that commitment before it goes live.
How the diff works
| Colour | Meaning |
|---|---|
| Green | Key present in the new (right) JSON, absent in the original |
| Red | Key present in the original (left), removed in the new version |
| Amber | Key exists in both, but the value has changed |
| None | Identical in both payloads |
Practical limits
Arrays are compared by position index, not by content identity. If an API returns the same items in a different order, the diff will flag every element as modified. Sort both arrays before comparing if order is not significant. Nested objects are handled recursively, so a change deep inside a structure will surface at the correct path. For GDPR compliance checks, this is useful to confirm that a data migration did not inadvertently add or expose new personal data fields.
Workflow in CI/CD
Use this tool to eyeball differences during development, then capture the expected diff in contract tests for your pipeline. For config file comparisons, see also TOML to JSON if your configuration is written in TOML and your CI system expects JSON.