Spoken Letter for Alexa+

Spoken Letter lets a family record a story in their own voice and deliver it to a child far away. This public companion repository brings those delivered stories to Alexa+ as an MCP add-on, built for the Amazon App Dev 2026 hackathon (Alexa+ track, AWS Builder and Open Source mini challenges).

It contains a dual-era MCP server (2026-07-28 specification served alongside the 2025-era handshake Alexa+ sends), an OAuth 2.1 authorization server, a simulated Alexa+ client on AWS (Strands Agents, Bedrock, Transcribe, Polly), the Amazon packaging path, and a CDK deployment at alexa.spokenletter.com. The add-on is the parent's tool: it exposes only stories the parent has already delivered, and no child account, voice or data exists on this path.

Architecture

Alexa+ (Amazon, US, en-US)                   Simulated Alexa+ client (judges, Owner)
   │ OAuth 2.1 auth code + PKCE                  │ browser SPA at https://alexa.spokenletter.com/demo
   │ Streamable HTTP, legacy initialize          │ mic → agent API → Transcribe streaming
   ▼                                             ▼
https://alexa.spokenletter.com  (CloudFront → Lambda function URL, RESPONSE_STREAM, Hono)
   ├── /mcp                      createMcpHandler (2026-07-28 + legacy 'stateless'), bearer JWT
   ├── /.well-known/oauth-protected-resource      RFC 9728 → issuer = same host
   ├── /.well-known/oauth-authorization-server    RFC 8414
   ├── /.well-known/jwks.json    KMS asymmetric public key
   ├── /oauth/authorize|token|continue|revoke     packages/oauth, DynamoDB tables
   ├── /bridge/link/complete|revoke              bearer ALEXA_BRIDGE_SECRET, called by Spoken Letter
   ├── /agent/*                 packages/agent: Strands + Bedrock, Polly, Transcribe (Lambda)
   └── /demo/*                  packages/simulator static SPA (S3 origin)

Agent → AgentCore Gateway (MCP server target, outbound client_credentials) → /mcp
Alexa+ → /mcp directly (Amazon requires the server itself)

Related MCP server: twine-mcp

Amazon tools used

Filled in per phase. Every entry does real work in code and has a friction-log entry.

Quick start

Requirements: Node.js 24, pnpm 11, and for Phase 6 onward the AWS CLI with the archy profile. Python 3.11 or newer runs the cc-rpi lifecycle scripts under .rpi/.

pnpm install
pnpm typecheck && pnpm lint && pnpm test && pnpm -F infra synth

The same four commands, plus the simulator's Playwright smoke (pnpm test:e2e), are the single verify job in .github/workflows/verify.yml. The complete local gate is declared in .rpi/policy.json and run by python3 .rpi/scripts/rpi-verify.py.

Run the MCP server locally on :4310 (prints a one-time MCP_DEV_TOKEN unless one is set):

pnpm dev
curl -s -X POST http://localhost:4310/mcp \
  -H "authorization: Bearer $MCP_DEV_TOKEN" -H "content-type: application/json" \
  -H "accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"list_family_stories","arguments":{}}}'

The whole link flow can be driven locally without the private repository:

DEV_ROUTES=1 PROVIDER_MODE=auto pnpm dev                       # prints ALEXA_BRIDGE_SECRET once
ALEXA_BRIDGE_SECRET=<printed> node scripts/mock-spoken-letter.mjs   # :3007, stands in for Spoken Letter
node scripts/e2e-link.mjs                                       # authorize → confirm → code → JWT → tools

Open http://localhost:4310/dev/start in a browser for the same flow by hand. Copy .env.example to .env to pin the generated values.

The simulated Alexa+ client runs with pnpm dev (server on :4310, Vite on :5173/demo/, AWS credentials from the archy profile for Bedrock, Polly and Transcribe) or pnpm dev:offline (scripted model, canned transcript, no AWS). pnpm test:e2e runs the Playwright smoke against the simulator's in-app mock.

Deploy (Owner, Phase 6 onward): pnpm deploy. Release procedure: docs/release.md.

Real device (Phase 9): a thin classic Alexa Skill in packages/skill calls the same agent endpoint and plays the family MP3 through AudioPlayer on an Echo. pnpm -F skill generate rebuilds the interaction model from the tool metadata; pnpm -F skill deploy creates the development-stage skill with the ASK CLI (Owner gate); pnpm -F skill record:pull collects real phrasings while RECORD_UTTERANCES=1.

Repository layout

packages/shared      env parsing, JSON logger, vendored agent-tool contract
packages/mcp-server  dual-era MCP server, fixture provider, three read-only tools (Phase 1)
fixtures/            the Owner's recorded stories for the demo subject (see fixtures/README.md)
packages/oauth       OAuth 2.1 authorization server: PKCE, client_credentials, RFC 8414/9728, JWT verifier (Phase 2)
                     app.ts composes OAuth + JWT-gated /mcp + dev routes; HttpProvider talks to the bridge (Phase 4)
packages/agent       Strands + Bedrock agent loop, scripted offline model, Polly, Transcribe, sessions (Phase 5)
packages/simulator   simulated Alexa+ SPA: Vite + React, brand tokens, Playwright smoke (Phase 5)
packages/app         the composed server: OAuth + MCP + agent on one Hono app; local and Lambda entry points
packages/skill       classic Alexa Skill front end for real-device footage: handler, agent client, generated interaction model (Phase 9)
infra/               CDK app: Core, Simulator, Api, Edge, Gateway, Observability, Skill stacks; bundle and seed scripts
amazon/              addon.json, agent-skill placeholder, runbook, US account checklist, Inspector guide (Phase 7)
scripts/             mock-spoken-letter.mjs (stand-in for the private bridge), e2e-link.mjs, verify-deploy.mjs, add-fixture-story.mjs
docs/                research, plans, decisions, friction log, product feedback, release

Built during the hackathon window

Everything in this repository was created between 2026-09-03 (plan) and the submission date, on the public develop and main branches. The dated history lives in docs/plans/2026-09-03-alexa-plus-mcp-add-on-notes.md (one handoff per phase, every review finding and its disposition, and the deviation register D1 to D21) and in docs/friction-log.md. The private Spoken Letter repository receives only the small bridge described in Phase 3 of the plan, after its freeze lifts on 2026-10-01; that pull request is linked here when it exists.

Manual latency workflow: .github/workflows/latency.yml runs scripts/verify-deploy.mjs from a us-east-1 runner against the deployed host (never deploys).

Working in this repository

Agent workflow follows cc-rpi (Research, Plan, Implement, Validate). Shared project facts and boundaries are in AGENTS.md; Claude Code reads them through CLAUDE.md.

• Plan: docs/plans/2026-09-03-alexa-plus-mcp-add-on.md and its phase files.

• Research: docs/research/. Decisions: docs/decisions/.

• Friction log: docs/friction-log.md. Product feedback: docs/product-feedback.md.

Licence

MIT. See LICENSE.