testland/mountebank-imposters
Authors Mountebank imposters (multi-protocol mock servers - HTTP, HTTPS, TCP, SMTP, LDAP, gRPC, WebSockets, GraphQL, and more) by POSTing JSON definitions to the Mountebank control API on port 2525, configures stubs with predicates and responses, and uses record-playback proxy mode to capture upstream traffic. Use when the project needs a multi-protocol mock server beyond HTTP-only tools like WireMock or MSW.
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predicates-and-proxying.mdreferences/
Mountebank predicate operators and proxying
Reference detail for mountebank-imposters: the full predicate-operator set and the record-playback proxy modes.
Predicate operators
Mountebank supports several predicate operators in addition to
equals:
| Operator | Meaning |
|---|---|
equals | Exact match. |
deepEquals | Deep equality on a nested object (e.g. JSON body). |
contains | Substring / partial match. |
startsWith / endsWith | Affix matchers. |
matches | Regex match. |
exists | Whether a field is present. |
not | Negate a child predicate. |
or | Boolean OR. |
and | Boolean AND. |
inject | Custom JavaScript predicate. |
Proxying for record-playback
Set up an imposter as a proxy to a real upstream:
{
"port": 4545,
"protocol": "http",
"stubs": [{
"predicates": [{ "matches": { "path": ".*" } }],
"responses": [{
"proxy": {
"to": "https://real-upstream.example.com",
"mode": "proxyOnce"
}
}]
}]
}| Mode | Behavior |
|---|---|
proxyOnce | First request hits upstream; response is stored as a stub; subsequent identical requests replay. |
proxyAlways | Every request hits upstream; every response is stored. |
proxyTransparent | Pass-through; nothing recorded. |
proxyOnce is the canonical record-playback workflow - run tests
once against a real upstream to populate the imposter, then run
forever offline.