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Concepts

Rift is a high-performance mock server. It speaks the Mountebank API for compatibility, but it is a tool in its own right — with a stateful model (flow-state, scenarios, correlated isolation) that goes well beyond record/replay. This section explains the mental model once, conceptually, so the reference and feature pages make sense.

Start here if you're new to Rift; jump to the reference pages when you need the exact syntax.

The two layers

Rift configuration has two layers that compose:

  1. The Mountebank layer — imposters, stubs, predicates, responses, and behaviors. If you know Mountebank, this is unchanged, and your existing configs work as-is. See Core Building Blocks.
  2. The Rift layer (_rift) — stateful and fidelity features Rift adds on top: flow-state, scenarios, correlated isolation ("spaces"), fault injection, scripting, and response templating. See The Rift Model.

Everything Rift-specific lives under a _rift key (imposter- or response-level) or under Rift-recognised stub fields, so a plain Mountebank config never collides with it.

The request lifecycle

When a request reaches an imposter, Rift:

  1. Accepts the connection. Usually on the imposter's own port, but a request can also arrive through the front door or the single-port gateway, which dispatch it in-process to the same imposter. For https imposters Rift terminates TLS here — and, with mutualAuth, demands a client certificate (TLS). HTTP/1.1 or HTTP/2 is settled per connection, by ALPN over TLS or by the connection preface in cleartext.
  2. Records the request in the imposter's journal when recordRequests is on — before matching, so a request that matches nothing is still visible.
  3. Matches it against each stub's predicates and picks the first stub, in declaration order, whose predicates all pass. With the X-Rift-Debug header, Rift explains the match instead of serving it (Debug Mode). If nothing matches, the imposter's defaultForward or defaultResponse answers.
  4. Selects a response from that stub's responses (cycling through them, honoring repeat).
  5. Resolves the response — a static is (with ${request.*} interpolation and templates), a proxy to an upstream, or a script/inject — and applies any fault injection.
  6. Runs behaviors — latency (wait), copy/lookup, and decorate/shellTransform transforms — before sending. (See Behaviors for the exact order.)

State (flow-state, scenario state, response cursors) is read and written along the way, keyed by the request's flow id.

Everything above belongs to the imposter. The intercept proxy is a separate listener in front of all of this: it terminates a CONNECT tunnel with a certificate signed by its own CA, matches each decrypted request against its own rules with the same predicate engine, and either serves an inline stub or forwards the request into an imposter, where the lifecycle above applies. An embedder can veto or replace a live exchange through the ExchangeInspector hook, which sees the request between steps 2 and 3 and the finished response after step 6.

In this section

  • Core Building Blocks — imposters, stubs, predicates, responses, behaviors.
  • The Rift Model — flow id, flow-state, scenarios, and correlated isolation (spaces), and how they fit together.