Anthropic

Lightweight, dependency-free, in-memory Anthropic Messages API fake for testing code that uses the real @anthropic-ai/sdk (and the language-agnostic Anthropic REST API). All generated content is deterministic — text is derived from a hash of the input so tests are repeatable.

Default port: 4748

Quick start

import { AnthropicServer } from "./services/anthropic/src/server.js";

const server = new AnthropicServer(4748);
await server.start();
// ... run your app/tests ...
await server.stop();

Point the real @anthropic-ai/sdk client at it via baseURL:

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  apiKey: "sk-ant-parlel",
  baseURL: "http://127.0.0.1:4748",
});

const message = await client.messages.create({
  model: "claude-3-5-sonnet-20241022",
  max_tokens: 256,
  messages: [{ role: "user", content: "Hello, Claude" }],
});
// message.content[0].text => deterministic text for that prompt
// message.request_id => "req_..." (matches real API)

Implemented operations

Authentication uses the x-api-key header (any non-empty key is accepted by design). The anthropic-version header is accepted but not enforced. State is in-memory and ephemeral.

• POST /v1/messages — create a message. Supports stream: true via the Anthropic SSE event format: message_start, content_block_start, ping, content_block_delta (text_delta), content_block_stop, message_delta, message_stop. Returns { id, type: "message", role: "assistant", content: [{ type: "text", text }], model, stop_reason, stop_sequence, usage, request_id }.
• POST /v1/messages/count_tokens — count tokens in a message. Validates messages and model fields. Returns { input_tokens, input_tokens_details: { cache_read, cache_creation }, request_id }.

Response metadata

All responses include a request-id HTTP header (format: req_<hex>) and a request_id field in the JSON body, matching the real Anthropic API. Error envelopes follow the real shape: { type: "error", error: { type, message }, request_id }.

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 anthropic

client = anthropic.Anthropic(api_key="sk-ant-parlel", base_url="http://127.0.0.1:4748")

with client.messages.stream(
    model="claude-3-5-sonnet-20241022",
    max_tokens=256,
    messages=[{"role": "user", "content": "Stream me"}],
) as stream:
    for text in stream.text_stream:
        print(text, end="")

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. Set ANTHROPIC_BASE_URL to 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.

Manifest

See services/anthropic/manifest.json:

• name: anthropic, image: parlel/anthropic:1
• port: 4748, protocol: http, healthcheck: /health, startup ≈ 100ms
• env: ANTHROPIC_API_KEY, ANTHROPIC_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.

ANTHROPIC_API_KEY=sk-ant-parlel
ANTHROPIC_BASE_URL=http://parlel-bridge:4748