OpenAPI Mocker

A self-contained Go application for a mock server based on OpenAPI contracts: project management, contract upload/edit/generation, manually and LLM-generated mock data, built-in web UI, and Go server/client code generation. Builds into a single binary / single Docker image and runs equally well on a desktop, in Docker, and in Kubernetes.

Features

1. Runs on desktop (go run/binary), in Docker, in Kubernetes.
2. Web UI in the browser (embedded SPA, nothing to deploy separately).
3. Projects: create, list, delete.
4. Contract: upload via file (YAML/JSON), manual editing in the browser, server-side validation against the OpenAPI 3.x spec. Publication = live immediately: the mock engine (MockServingService) always serves the latest saved version of the contract, so as soon as a contract is published, all endpoints described in it are immediately available at /mock/{projectId}/... — no separate "deploy" step. Versioning and change history: every save creates a new immutable version (history is never rewritten); in the UI you can view any old version, a line-by-line diff of a version against the current active one, and roll back to an old version (rollback also publishes a new version with that content — endpoints go live immediately).
5. Mock data: manual editing of body/status/headers/delay, or generation via LLM taking into account the endpoint's JSON Schema.
6. LLM providers: OpenAI, Azure OpenAI, Anthropic, Google Gemini, Ollama, vLLM, LM Studio, Groq, OpenRouter, Together, DeepSeek + arbitrary custom HTTP provider. Providers can be global or bound to a project.
7. OpenAPI contract generation from a text description via LLM + validation (including targeted validation of the mock body against the contract's response schema).
8. Go server and Go client code generation in one click (download as zip).
9. Additional features:
   • Response scenarios (X-Mock-Scenario) — multiple response variants for one endpoint (happy path, empty, error…), selected by a header.
   • Delay simulation and chaos error injection (delayMs, failRatePct) — for testing client resilience.
   • Schema-example fallback, used when a mock is not configured manually or via LLM — the endpoint always responds with something valid.
   • Request log to the mock server (method/path/status/time) right in the UI.
   • "Try it" in the browser — sending a request to the mock without Postman/curl.

Quick start (desktop)

go mod tidy   # requires network access - downloads kin-openapi
go run ./cmd/server
# UI:  http://localhost:8080

Docker

cd deploy
docker compose up --build
# UI:  http://localhost:8080

or manually:

docker build -f deploy/Dockerfile -t openapi-mocker:latest .
docker run -p 8080:8080 -v mocker-data:/data openapi-mocker:latest

Kubernetes

kubectl apply -f deploy/k8s/00-namespace.yaml
kubectl apply -f deploy/k8s/
# (the image must be reachable by the cluster: docker build + push to your
#  registry, then fix image: in deploy/k8s/03-deployment.yaml)
kubectl -n openapi-mocker port-forward svc/openapi-mocker 8080:80

REST API (summary)

Method / Path	Purpose
GET/POST /api/projects	list / create project
GET/DELETE /api/projects/{id}	project
GET/POST /api/projects/{id}/contract	get / publish active contract
GET /api/projects/{id}/contract/versions	version history
GET /api/projects/{id}/contract/versions/{version}	contents of a specific version
POST /api/projects/{id}/contract/versions/{version}/rollback	roll back to a version (re-publishes it)
GET /api/projects/{id}/contract/diff?from=X&to=Y	line-by-line diff of two versions (to defaults to current)
POST /api/projects/{id}/contract/validate	validate contract
POST /api/projects/{id}/contract/generate	generate contract via LLM
GET /api/projects/{id}/endpoints	list contract operations
GET/POST /api/projects/{id}/mocks	list / create mock rules
PUT/DELETE /api/mocks/{mockId}	edit / delete a mock rule
POST /api/projects/{id}/mocks/generate	generate mock body via LLM
GET/POST /api/llm-providers	global LLM providers
GET /api/projects/{id}/llm-providers	providers available to the project
PUT/DELETE /api/llm-providers/{id}	edit / delete provider
POST /api/llm-providers/{id}/test	connection test
GET /api/projects/{id}/codegen/server	download Go server zip
GET /api/projects/{id}/codegen/client	download Go client zip
GET /api/projects/{id}/logs	recent mock requests
ANY /mock/{projectId}/**	the mock server itself (by project contract)

curl -H "X-Mock-Scenario: error" http://localhost:8080/mock/<projectId>/users/1

Known limitations / roadmap

• The JSON-file store (internal/adapter/repository/jsonstore) is not suited for multiple replicas — for HA, add an adapter over a real DB implementing the same 5 interfaces from internal/usecase/ports.go; the usecase and HTTP layers won't need changes.
• Code generation currently covers Go only; for other languages it makes sense to integrate openapi-generator-cli as a separate CI/CD step, or implement usecase.CodeGenerator with another adapter.
• No role model / authentication — the application is assumed to live behind a corporate VPN/ingress with its own auth (e.g. oauth2-proxy in front of the Ingress).
• LLM provider API keys are stored in the data file in plaintext — for production, encrypt them at rest or feed them in through a Kubernetes Secret and a separate protected endpoint.