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Rules let one route return different responses depending on the incoming request, without writing any code. On the Rules sub-tab of a response, you add one or more conditions; the response is served only when they are satisfied. Rules are how Rules-based and Fallback selection decide which response to pick. A response with no rules is served unconditionally, which is exactly what you want for the catch-all default response.

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Anatomy of a rule

Each rule has five parts:
  • A target: what part of the request to inspect. Method, Path, Query, Header, Body (matched with a JSONPath expression), Cookie, or URL Param.
  • A property: which key or path within the target to read, for example a header name, a query key, or a $.json.path into the body.
  • An operator: equals, contains, regex, >, <, in, exists, or jsonpath.
  • A value to compare against.
  • An invert toggle to negate the match (NOT).
The Rules sub-tab of a mock response showing a rule row with target, property, operator, value, and invert controls
When a response has more than one rule, combine them with the AND / OR toggle. With AND, every rule must pass; with OR, any one passing is enough. You set one combinator per response.
Body and header matching are on by default, so you can match against request body fields and header values out of the box without any extra setup. The Body target uses a dot-path existence check (for example, does user.role exist), not full JSONPath filters.

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Add a rule

1

Open the response's Rules tab

In the response pane, select the response you want to gate, then open its Rules sub-tab.
2

Add and configure a condition

Add a rule, then set its target, property, operator, and value. Turn on invert if you want the rule to match when the condition is not met.
3

Combine multiple rules

If you added more than one rule, set the AND / OR toggle to decide whether all of them or any of them must pass.
4

Save and test

Click Save, make sure the mock is running, then call the endpoint with and without the matching condition to confirm the right response is served.

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Worked examples

Each example below gates a response on a real condition and shows the served result.

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Require a header (exists + invert)

To return a 403 only when the Authorization header is missing, add a 403 response with one rule: target Header, property authorization, operator exists, invert on. Mark the normal 200 response as default.
The missing header matches the inverted exists rule and returns 403; a present header falls through to the default 200.

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Match on the request body (JSONPath)

To branch on the shape of a JSON body, use the Body target with the jsonpath operator. Here a POST /orders response is gated on $.user.role existing, with a 422 default:

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Read a URL parameter (equals)

A URL Param rule reads a value captured by a :param in the path. Here GET /accounts/:id serves a special response only when id equals 42:

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Combine rules with AND

With the combinator set to AND, every rule must pass. Here a response on GET /and requires both ?a=1 and ?b=2:

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Combine rules with OR

With the combinator set to OR, any one rule passing is enough. Here a response on GET /or matches when either ?a=1 or ?b=2: