PostHog

Lightweight, dependency-free, in-memory PostHog API fake for testing code that uses the real posthog-node / posthog-js SDKs (and the language-agnostic PostHog REST API).

Default port: 4807

Quick start

import { PosthogServer } from "./services/posthog/src/server.js";

const server = new PosthogServer(4807);
await server.start();
// ... run your app/tests ...
await server.stop();

Point the real posthog-node client at it via the host option:

import { PostHog } from "posthog-node";

const client = new PostHog("phc_parlel_test_key", {
  host: "http://127.0.0.1:4807",
});

client.capture({ distinctId: "user-123", event: "user signed up", properties: { plan: "pro" } });
await client.flush();

Every captured event is held in memory and can be inspected via the /__parlel/* endpoints.

Implemented operations

Event ingestion uses the project api_key in the request body (no bearer required). The /api/* REST surface requires Authorization: Bearer <personal-api-key>.

Event ingestion

• POST /capture/ — ingest a single event. Returns 200 { status: 1 }.
• POST /batch/ — ingest a batch ({ batch: [...] }). Returns 200 { status: 1 }.
• POST /e/, POST /i/ — posthog-js ingest aliases (route to capture).
• POST /decide/ — feature flag evaluation. Returns { featureFlags, featureFlagPayloads, config, ... }.

Project REST API (/api/projects/:id)

• GET /api/projects/:id/insights — list insights ({ count, results: [...] }).
• POST /api/projects/:id/insights — create an insight (201).
• GET|PATCH|DELETE /api/projects/:id/insights/:insightId — read / update / delete.
• GET|POST /api/projects/:id/events — query captured events (optional ?event= filter).
• GET /api/projects/:id/feature_flags — list feature flags.

Service & inspection operations (parlel extensions)

• GET / — service metadata.
• GET /health — health check ({ status: "ok" }).
• POST /__parlel/reset — reset all in-memory state.
• GET /__parlel/events — list every captured event ({ events, count }).
• DELETE /__parlel/events — clear captured events.
• POST /__parlel/feature_flags — set a flag value ({ key, value }).
• OPTIONS * — CORS preflight (204).

Access via MCP / preview URL

When run inside a parlel pool, the service is reachable at its preview URL (the host/port shown by the pool). Configure your SDK's host to that URL. Through the parlel MCP server, the service is exposed as a tool surface so an AI agent can drive captures and query events without leaving the editor — the same /capture/, /batch/, /decide/ and /api/projects/:id/* routes are available.

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.

Manifest

See services/posthog/manifest.json:

• name: posthog, image: parlel/posthog:1.0
• port: 4807, protocol: http, healthcheck: /health, startup ≈ 100ms
• env: POSTHOG_API_KEY, POSTHOG_PERSONAL_API_KEY, POSTHOG_HOST

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.

POSTHOG_API_KEY=phc_parlel
POSTHOG_PERSONAL_API_KEY=phx_parlel
POSTHOG_HOST=http://parlel-bridge:4807
POSTHOG_BASE_URL=http://parlel-bridge:4807