Can I apply multiple transformation rules in a single policy?

Yes. A single Response Transformer Policy can contain multiple transformation rules, each targeting a different field or header. Rules are applied in the order they are defined.

What is the difference between Replace and Upsert?

Replace updates the value of an existing field and leaves it unchanged if the field does not exist. Upsert adds the field if it does not exist, or updates it if it does.

Can I transform the response body and headers in the same policy?

Yes. Each transformation rule specifies its own Location (Header or Body), so you can mix header and body transformations within a single policy.

Does the policy affect error responses from the backend?

Yes, the policy applies to all responses matching the configured protocols, including error responses. Use protocol or condition filtering to limit which responses are transformed.

Response Transformer Policy- UnifyApps

Modify API responses before they reach the client by adding, removing, renaming, or replacing headers and body fields.

Overview

A Response Transformer Policy modifies API responses before they are sent back to the client. Use it to add, remove, rename, or replace headers and body fields — for example, to standardize response formats, mask sensitive data, or adapt backend output to match what your clients expect without touching the backend service itself.

Field Reference

Field	Description
Policy Name *	A unique identifier used across logs, dashboards, and API group configurations.
Tags	Custom labels to organize and filter the policy by environment, team, or functionality.
Protocols *	The response protocols for which this policy applies (e.g., HTTP, HTTPS). Only matching responses trigger the policy.
Transformations *	One or more transformation rules. Each rule specifies an Operation, Location, Key, and Value.

Transformation Rule Fields

Sub-field	Description
Operation	Upsert — add or update a field; Remove — delete a field; Rename — rename an existing field; Replace — replace a field's value.
Location	Header — modify HTTP response headers; Body — modify the response payload.
Key	The field name to transform. For Header, the header name; for Body, the payload field name.
Value	For Upsert/Replace: the new value. For Rename: the new key name. For Remove: the field to delete.

How It Works

Response received from backend — The backend service returns a response to the gateway.
Policy evaluation — The response is checked against the configured protocols to determine if the policy applies.
Transformation execution — Each rule is applied in sequence: headers or body fields are added, updated, renamed, replaced, or removed per the configured location.
Modified response returned — After all transformations, the updated response is sent to the client.

Attaching to an API Group

Once a Response Transformer Policy is created, attach it to one or more API Groups from the group's policy settings. Multiple policies can be applied to a single group; drag them into the desired execution order.

Notes

Transformation rules are applied in the order you define them — if rules depend on each other (e.g., rename before replace), order them deliberately.
Use Remove to strip internal or sensitive fields (internal IDs, debug headers) before the response reaches clients.
Use Upsert to inject standard headers (e.g., X-API-Version) across all responses without changing every backend endpoint.
Test transformations against sample responses before attaching to a production group to confirm the output shape is what clients expect