SparkPost

Lightweight, dependency-free, in-memory SparkPost API v1 fake for testing code that uses the real sparkpost Node SDK (or the language-agnostic SparkPost REST API).

Default port: 4830

Quick start

Start the server:

import { SparkpostServer } from "./services/sparkpost/src/server.js";

const server = new SparkpostServer(4830);
await server.start();
// ... run your app/tests ...
await server.stop();

Point a client at it. SparkPost uses a raw Authorization header (no Bearer prefix):

await fetch("http://127.0.0.1:4830/api/v1/transmissions", {
  method: "POST",
  headers: { Authorization: "parlel-sparkpost-key", "Content-Type": "application/json" },
  body: JSON.stringify({
    content: { from: "sender@parlel.dev", subject: "Hello", html: "<b>Hi</b>" },
    recipients: [{ address: { email: "recipient@parlel.dev" } }],
  }),
});
// => { results: { total_rejected_recipients: 0, total_accepted_recipients: 1, id } }

Every send is captured and inspectable via /__parlel/*.

Access via MCP / preview URL

When run under the parlel pool, this service is reachable through the MCP gateway and a preview URL at http://127.0.0.1:4830. Use SPARKPOST_BASE_URL to point clients/agents at it. Captured mail lives at GET /__parlel/messages.

Implemented operations

All /api/v1/* routes require a raw Authorization: <api-key> header. State is in-memory and ephemeral.

• POST /api/v1/transmissions — send a transmission (content.from, recipients[].address.email). Captures and returns { results: { total_rejected_recipients, total_accepted_recipients, id } }.
• GET /api/v1/transmissions — list transmissions.
• GET /api/v1/transmissions/:id — retrieve a transmission.
• GET /api/v1/templates — list templates.
• POST /api/v1/templates — create a template (id + content required).
• GET /api/v1/account — account info.

Service & inspection operations (parlel extensions)

• GET / — service metadata.
• GET /health — health check ({ status: "ok" }).
• POST /__parlel/reset — reset all in-memory state.
• GET /__parlel/messages — list captured messages ({ messages, count }).
• GET /__parlel/messages/:id — fetch a single captured message.
• DELETE /__parlel/messages — clear only the captured mailbox.

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.

Error shapes

Errors use the SparkPost envelope { "errors": [{ "message", "code", "description" }] }.

Manifest

See services/sparkpost/manifest.json:

• name: sparkpost, image: parlel/sparkpost:1.0
• port: 4830, protocol: http, healthcheck: /health, startup ≈ 100ms
• env: SPARKPOST_API_KEY, SPARKPOST_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.

SPARKPOST_API_KEY=parlel-sparkpost-key
SPARKPOST_BASE_URL=http://parlel-bridge:4830