AssemblyAI
Lightweight, dependency-free, in-memory AssemblyAI API fake for testing code that uses the real assemblyai Node.js SDK (and the language-agnostic AssemblyAI REST API).
Default port: 4858
Quick start
import { AssemblyaiServer } from "./services/assemblyai/src/server.js";
const server = new AssemblyaiServer(4858);
await server.start();
// ... run your app/tests ...
await server.stop();
Point the real assemblyai client at it via baseUrl:
import { AssemblyAI } from "assemblyai";
const client = new AssemblyAI({ apiKey: "parlel_assemblyai", baseUrl: "http://127.0.0.1:4858" });
const transcript = await client.transcripts.transcribe({ audio_url: "https://x/a.wav" });
// transcript.status === "completed", transcript.text => deterministic text
Transcripts, uploads, and LeMUR responses are deterministic: derived from a hash of the input. Transcripts complete on the first GET.
Access via MCP / preview URL
- Base URL:
http://127.0.0.1:4858 - Health:
GET /health→{ "status": "ok" } - Auth header:
Authorization: <key>(raw key, no scheme — any non-empty value accepted).
Implemented operations
POST /v2/upload— upload raw audio bytes (application/octet-stream) →{ upload_url }.POST /v2/transcript— create a transcript from{ audio_url }→{ id, status: "queued", ... }.GET /v2/transcript— list transcripts with pagination →{ transcripts: [...], page_details: { limit, result_count, current_url, prev_url, next_url } }.GET /v2/transcript/:id— poll; completes on first GET →{ status: "completed", text, words: [...] }.DELETE /v2/transcript/:id— delete a transcript → returns the deleted transcript object.POST /lemur/v3/generate/task— LeMUR custom task from{ prompt, transcript_ids }→{ request_id, response, usage }.
Service & inspection operations (parlel extensions)
GET /— service metadata.GET /health— health check.POST /__parlel/reset— reset state.GET /__parlel/transcripts— list captured transcripts.
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 |
|---|---|
transcripts.create / get | ✅ Supported |
transcripts.list (GET /v2/transcript) | ✅ Supported |
transcripts.delete (DELETE /v2/transcript/:id) | ✅ Supported |
files.upload (/v2/upload) | ✅ Supported |
LeMUR generate/task | ◐ Accepted — deprecated endpoint, emulated for backward compat |
| Deterministic transcripts/responses | ✅ Supported |
| Full transcript response fields (speech_model, language_model, etc.) | ✅ Supported |
| Real speech recognition | ✓ By design — Intentionally unsupported (hash-derived) |
| Realtime/streaming transcription | ⟳ Roadmap |
| Polling delay (queued→processing→completed) | ◐ Completes immediately on first GET |
| Key validity / quota | ✓ By design — Never throttles — local tests run at full speed, zero cost |
Error codes & shapes
Errors use { "error": "<message>" } — matching the real AssemblyAI API exactly.
| Status | When |
|---|---|
401 | missing/empty Authorization |
400 | missing audio_url/prompt or bad JSON |
404 | unknown transcript or endpoint |
500 | internal server error |
Manifest
See services/assemblyai/manifest.json:
- name:
assemblyai, image:parlel/assemblyai:1.0 - port:
4858, protocol:http, healthcheck:/health, startup ≈ 100ms - env:
ASSEMBLYAI_API_KEY,ASSEMBLYAI_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.
ASSEMBLYAI_API_KEY=parlel_assemblyai
ASSEMBLYAI_BASE_URL=http://parlel-bridge:4858