Built on an existing server
The project extends the open-source ryaker/outlook-mcp server. The additions here are the CLI front end, the shared tool registry, attachment handling, the jest test suite, and npm packaging.
Outlook CLI
An npm CLI and stdio MCP server for Outlook mail and calendar over Microsoft Graph: one OAuth login, one tool registry shared by humans and agents.
- Role
- Extended and published
- Where
- Independent project
- When
- Apr 2026
- Access
- Public repo · npm
Problem
Managing Outlook from a terminal or an agent usually means an OAuth dance on every run and output written only for humans. The tool needed one login, reusable tokens, and output an agent can parse, with the same behaviour whether a person or an assistant is calling it.
01
Two front doors, one behaviour
The terminal CLI and the stdio MCP server both call the same frozen tool registry, so a command and the matching agent tool cannot drift apart.
02
Log in once
The first call opens a delegated-permission OAuth flow in the browser and saves the tokens locally. Every later call reuses them and refreshes them when they expire.
03
21 tools across four domains
Mail (including attachments), calendar, folders, and inbox rules, each a handler behind the shared registry.
04
Graph, or a mock
Every request goes through one Graph client, and a test-mode switch swaps in mock data so the suite runs without an account.
05
Output for people and for agents
The CLI renders themed tables for people and switches to machine-readable output with --json or --ai.
Measured
- MCP tools
- 21
- jest tests
- 65
- Front ends sharing one registry
- 2
- Runtime dependencies
- 3
How it's verified
- Harness
- One frozen tool registry behind both the terminal CLI and the stdio MCP server.
- Guardrails
- Delegated OAuth scopes only; a test mode swaps in mock data so the suite never touches a real mailbox.
- Testing
- 65 jest tests; publishing runs the suite and a dry-run pack first.
In depth
Publishing with checks
Publishing runs the test suite and a dry-run pack first, so a broken build or a missing file never reaches npm.
Decisions
- 01One registry for both interfaces, so humans and agents get identical behaviour.
- 02Machine-readable output as a first-class mode, not an afterthought.
- 03A deliberately small dependency surface: the MCP SDK, chalk, and dotenv.
Stack
Node.js · MCP SDK · Microsoft Graph · OAuth 2.0 · jest · npm