---
title: Twelve Month Calendar
description: Agent-readable product overview and integration entry point.
canonical: https://twelvemonthcalendar.com/
last-updated: 2026-09-01
---

# 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, remove, restore, or filter events in their Twelve Month Calendar; compare commitments across a whole year; isolate one person's travel; 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 MCP tool catalog is public so an agent can understand the available operations. Private calendar reads and writes require a user-authorized OAuth access token or, for clients without OAuth, a scoped personal access token. Resolve exact resource IDs before mutations, send a stable idempotency key, and use the latest resource version for updates or deletes.

## Authentication and permissions

Prefer OAuth for agents: 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. Personal access tokens are a fallback for scripts or clients that cannot complete OAuth. A 401 response means a 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 and may reference any number of categories, people, and tags. Saved views combine include and exclude filters, person matching, tag matching, conflict rules, and a color mode. The year-overview endpoint returns 365 or 366 numberless day projections with workload, conflict, accessible labels, and compact event previews. All writes return an activity record and use optimistic concurrency. Deleted resources remain restorable during their retention window.

## Integration sequence

1. Read the OpenAPI schema or list the public MCP tools.
2. Connect through discovered OAuth metadata and hand browser consent to the user; never ask the user to paste an OAuth credential into chat.
3. List calendars, categories, people, tags, or saved views to resolve exact IDs.
4. Read the target event before changing or deleting it.
5. Send a stable idempotency key and the latest expected version with every mutation.
6. Report the resulting event, warning, and request identifier to the user.