Imposter
Imposter is an open-source tool for creating interactive mock systems for development and QA.
What Imposter is
Imposter is an open-source tool for creating interactive mock systems for development and QA. It can turn OpenAPI files, WSDL files, or REST endpoints into mock APIs, with documented support for REST, OpenAPI/Swagger, SOAP/WSDL, HBase, Salesforce, and WireMock mappings. Mocks can run as standalone services in Docker, Kubernetes, AWS Lambda, or on the JVM, or be embedded in JVM and Node.js tests. Responses may come from static files or vary with requests, using JavaScript, Groovy, or Java scripts and custom plugins in JVM languages. The OpenAPI plugin can validate request parameters, headers, and bodies against a specification. Imposter can capture request data for later retrieval or templated replies, and proxy an existing endpoint to replay its responses. The documentation includes CI/CD use with GitHub Actions, GitLab CI, CircleCI, Jenkins, and Azure Pipelines. HTTPS with TLS and request authentication are configurable. The core Docker image includes OpenAPI, REST, and SOAP plugins; the all image contains every plugin and has more dependencies.
Good
- Creates mocks from OpenAPI, WSDL, or REST endpoints.
- Supports request-dependent responses and scripting.
- Can validate requests against OpenAPI specifications.
- Runs standalone or embedded in JVM and Node.js tests.
- Can capture request data and proxy existing endpoints.
Watch out
- The all Docker image has more dependencies.
- The core Docker image includes only OpenAPI, REST, and SOAP plugins.
- Shell-script CLI installation is for macOS and Linux.
Who it suits
Imposter suits developers and QA teams that need mock APIs or systems for development and testing. It may be useful for teams seeking to decouple integration tests from cloud or backend systems.
Verdict
Imposter offers flexible mock creation, deployment, and request handling for development and QA workflows. The Docker image choice matters: the core image has fewer plugins, while the all image brings more dependencies.
The facts
Each one read from Imposter's own pages, with the date it was checked.
What it does
- API validation and proxying
- It can validate requests against an OpenAPI specification and proxy an existing endpoint to replay its responses as a mock.checked 4 Oct 2026
- Audience
- The maker presents Imposter for developers, including API developers, and highlights development and QA use cases.checked 3 Oct 2026
- CI/CD
- The getting started guide describes using Imposter in GitHub Actions and other CI/CD platforms, including GitLab CI, CircleCI, Jenkins, and Azure Pipelines.checked 3 Oct 2026
- Data capture and proxying
- Imposter can capture request data for later retrieval or templated responses, and proxy an existing endpoint to replay its responses as a mock.checked 3 Oct 2026
- Distribution limit
- The Docker documentation says the core image includes OpenAPI, REST, and SOAP plugins, while the all image contains all plugins and has the most dependencies.checked 4 Oct 2026
- Dynamic responses
- Responses can use static files or be scripted with JavaScript, Groovy, or Java; advanced users can write plugins in JVM languages.checked 4 Oct 2026
- Integrations
- The CLI documentation describes embedding Imposter in JVM and Node.js tests, and using GitHub Actions or other CI/CD platforms including GitLab, CircleCI, Jenkins, Azure Pipelines, and Bitbucket.checked 4 Oct 2026
- Intended users
- The maker describes Imposter as a tool for developers and QA, including teams that want to decouple integration tests from cloud or backend systems.checked 4 Oct 2026
- Pricing
- The opened maker pages describe the project and its downloads but do not state a price or subscription plan.checked 3 Oct 2026
- Purpose
- Imposter runs interactive mock systems for development and QA, including before a real API is available.checked 4 Oct 2026
- Request data
- Imposter can capture request data for later retrieval or use it in templates to create conditional responses.checked 4 Oct 2026
- Request validation
- The OpenAPI plugin can validate incoming request parameters, headers, and bodies against the specification.checked 3 Oct 2026
- Run modes
- Imposter can run as a standalone server in Docker, Kubernetes, AWS Lambda, or on the JVM, or be embedded in JVM and Node.js tests.checked 3 Oct 2026
- Security
- Imposter supports HTTPS through TLS configuration and can authenticate incoming HTTP requests using configured request conditions such as header values.checked 4 Oct 2026
- Supported APIs
- The documentation lists mock support for REST, OpenAPI/Swagger, SOAP/WSDL, HBase, Salesforce, and WireMock mappings.checked 3 Oct 2026
- Supported mocks
- It supports REST, OpenAPI/Swagger, SOAP/WSDL, HBase, Salesforce, and WireMock mappings.checked 4 Oct 2026
- Telemetry
- The feature documentation lists metrics collection and persistent or semi-persistent stores as configurable features.checked 3 Oct 2026
- Ways to run
- You can run standalone mocks in Docker, Kubernetes, AWS Lambda, or on the JVM, or embed them in JVM and Node.js tests.checked 4 Oct 2026
The company
- Maker
- The linked Gatehill site identifies Pete Cornish as the person who builds tools under the Gatehill name.checked 4 Oct 2026
Where it runs
- Platform support
- The CLI install page says its shell-script installation is for macOS and Linux; the CLI also supports native binary and Docker engines.checked 4 Oct 2026
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