---
title: Twelve Month Calendar
description: Agent-readable product overview and integration entry point.
canonical: https://twelvemonthcalendar.com/
last-updated: 2026-09-03
---

# Twelve Month Calendar

Twelve Month Calendar is a private, user-owned visual calendar that shows an entire year in one glanceable grid. It helps people compare travel, time off, hosting, milestones, work, family schedules, and potential conflicts without reading hundreds of labels.

## When to use this

Use Twelve Month Calendar when a user asks you to understand, add, change, or remove events in their Twelve Month Calendar; compare commitments across a whole year; or find potential calendar conflicts. Do not use it for a calendar the user has not authorized, and do not claim Google Calendar synchronization is available.

## Agent interfaces

- MCP Streamable HTTP: https://mcp.twelvemonthcalendar.com/mcp
- REST API: https://api.twelvemonthcalendar.com/v1
- OpenAPI 3.1: https://api.twelvemonthcalendar.com/v1/openapi.json
- MCP server card: https://mcp.twelvemonthcalendar.com/.well-known/mcp/server-card.json
- Authentication: https://twelvemonthcalendar.com/auth.md
- Permission scopes: https://twelvemonthcalendar.com/developers/scopes
- Detailed instructions: https://twelvemonthcalendar.com/agents.md
- Reusable skill: https://twelvemonthcalendar.com/skills/twelve-month-calendar/SKILL.md

The documentation index is https://twelvemonthcalendar.com/developers.md. The schema feed is https://twelvemonthcalendar.com/schema-feed.jsonl, the API catalog is https://twelvemonthcalendar.com/.well-known/api-catalog, the ARD catalog is https://twelvemonthcalendar.com/.well-known/ard.json, and the public NLWeb question endpoint is https://twelvemonthcalendar.com/ask.

The public OpenAPI contract and MCP server card describe the product operations. The public, read-only documentation MCP at https://mcp.twelvemonthcalendar.com/docs/mcp answers integration questions without credentials. Calendar-data REST calls and every product MCP protocol call require a user-authorized OAuth access token, including MCP initialization and tool discovery. Resolve exact resource IDs before mutations and use the latest resource version for updates or deletes.

## Authentication and permissions

Use OAuth for every agent: begin at the MCP or REST protected resource, follow its RFC 9728 metadata to the authorization server, use its advertised registration method, and complete Authorization Code with S256 PKCE and human browser consent. Ask only for the scopes required by the task, and never ask the user to create or paste a credential. A client that cannot complete OAuth is unsupported. A 401 response means an OAuth credential is missing or invalid; a 403 response means the credential lacks a requested scope or calendar grant; a 412 response means the resource version is stale.

## Data model and safety

Events belong to calendars, may have one category, and may reference any number of people. The year-overview endpoint returns all events as 365 or 366 dated day projections with workload, conflict, accessible labels, and compact event previews. Updates and deletes use optimistic concurrency, and deletion is permanent.

## Integration sequence

1. Read the public OpenAPI contract or MCP server card.
2. Connect through discovered OAuth metadata and hand browser consent to the user; never ask the user to paste a credential into chat.
3. After OAuth succeeds, initialize MCP and list tools, then list calendars, categories, people, or people groups to resolve exact IDs.
4. Read the target event before changing or deleting it.
5. Send the latest expected version with every update or deletion.
6. Report the resulting event, warning, and request identifier to the user.