Google Gemini

Lightweight, dependency-free, in-memory Google Gemini (Generative Language) API fake for testing code that uses the real @google/generative-ai / @google/genai SDKs (and the language-agnostic REST API). All generated content is deterministic — text is derived from a hash of the input so tests are repeatable.

Default port: 4749

Quick start

import { GoogleGeminiServer } from "./services/google-gemini/src/server.js";

const server = new GoogleGeminiServer(4749);
await server.start();
// ... run your app/tests ...
await server.stop();

Point the real SDK at it via a custom base URL:

import { GoogleGenerativeAI } from "@google/generative-ai";

const genAI = new GoogleGenerativeAI("parlel");
const model = genAI.getGenerativeModel(
  { model: "gemini-1.5-flash" },
  { baseUrl: "http://127.0.0.1:4749" },
);

const result = await model.generateContent("Hello Gemini");
// result.response.text() => deterministic text for that prompt

Implemented operations

Authentication uses either a ?key= query parameter or the x-goog-api-key header (any non-empty key is accepted). State is in-memory and ephemeral.

POST /v1beta/models/{model}:generateContent — generate content. Returns { candidates: [{ content: { parts: [{ text }], role: "model" }, finishReason, safetyRatings }], usageMetadata, modelVersion }.
POST /v1beta/models/{model}:streamGenerateContent — streaming. Default returns a JSON array of incremental chunks; pass ?alt=sse for the SSE data: line format.
POST /v1beta/models/{model}:countTokens — returns { totalTokens }.
GET /v1beta/models — list available models.

Service & inspection operations (parlel extensions)

GET / — service metadata.
GET /health — health check ({ status: "ok" }).
POST /__parlel/reset — reset all in-memory state.
GET /__parlel/requests — list captured requests.
DELETE /__parlel/requests — clear the captured request log.

SDK usage example

import google.generativeai as genai

genai.configure(api_key="parlel", client_options={"api_endpoint": "127.0.0.1:4749"})
model = genai.GenerativeModel("gemini-1.5-flash")
response = model.generate_content("Hello Gemini")
print(response.text)

Access via MCP / preview URL

HTTP services are auto-exposed at the Daytona preview URL. Send requests to the preview URL with the x-daytona-preview-token header for authentication. Point your Gemini base URL / endpoint at the preview URL.

Surface coverage

This emulator faithfully replicates the API surface most application code and agents exercise. Anything below the supported lines is either an intentional design choice for a fast, zero-cost local emulator (✓ By design) or a candidate for a future release (⟳ Roadmap) — never a silent inaccuracy.

Legend: ✅ fully supported · ◐ accepted (stored, not strictly enforced) · ✓ by design · ⟳ on the roadmap.

Feature	Status
`generateContent`	✅ Supported
`streamGenerateContent` (array + `alt=sse`)	✅ Supported
`countTokens`	✅ Supported
`models` list	✅ Supported
Both `?key=` and `x-goog-api-key` auth	✅ Supported
Request inspection	✅ Supported (parlel extension)
Real model inference / quality	✓ By design — Deterministic stub output — repeatable assertions, no API spend
Function calling / tools execution	◐ Accepted, not executed
Vision / inline data / file API	⟳ Roadmap
Token counts	◐ Approximate word-based
Safety rating computation	◐ Fixed `NEGLIGIBLE` placeholders
API key validity / quota	✓ By design — Never throttles — local tests run at full speed, zero cost

Manifest

See services/google-gemini/manifest.json:

name: google-gemini, image: parlel/google-gemini:1
port: 4749, protocol: http, healthcheck: /health, startup ≈ 100ms
env: GEMINI_API_KEY, GOOGLE_API_KEY, GEMINI_BASE_URL

Configuration — `test.env`

Copy these into your test.env (used by the bridge sidecar flow). Tokens are Parlel's seeded test credentials — any non-empty value is accepted by the emulator, so you rarely need to change them. Swap in real credentials only when pointing at the live service in prod.env.

GEMINI_API_KEY=parlel
GOOGLE_API_KEY=parlel
GEMINI_BASE_URL=http://parlel-bridge:4749