caldav-mcp - Calendar Operations over CalDAV for Agents¶

Local stdio MCP server (TypeScript, MIT) - caldav-mcp gives an MCP client read and write access to calendars over the CalDAV standard: events, tasks and journal entries on Radicale, Baikal, Nextcloud, SOGo, Fastmail, iCloud and hosted providers generally. It is part of the ni-c suite alongside imap-mcp (read mailbox) and smtp-mcp (send mail).

Server type: Local (stdio, TypeScript)
Auth: CalDAV account credentials; no vendor API
Install: npx @ni-c/caldav-mcp
Tools: 22 (10 read, 12 write); CALDAV_READ_ONLY=true unregisters the write tools
Pricing: Free software
Category: Productivity
Built by: ni-c (github.com/ni-c/caldav-mcp)

Why This Matters for Operators¶

Calendar data is scheduling truth, and agents that cannot touch it fall back to asking humans to read their own calendars aloud. caldav-mcp puts calendar operations in the agent's hands with the ni-c safety conventions: writes are read-modify-write guarded with If-Match so unknown properties, alarms and attendees survive edits; recurring events are expanded client-side with three independent bounds; and a CALDAV_CALENDARS fence confines the server to named calendars, enforced at the point where ids are decoded.

Calendar content is treated as untrusted input - a scheduling-enabled server lets anyone who knows your address write into your calendar - so returned content is fenced with a per-call nonce and nothing the server says in its own voice quotes it.

Tools & Capabilities¶

Group	What the agent does
Event operations	Read, create, update and delete events across the server's calendars
Tasks and journals	Task and journal entry management over VTODO and VJOURNAL
Recurrence	Client-side expansion of recurring events, bounded against pathological rules
Safety controls	CALDAV_READ_ONLY unregisters write tools; CALDAV_CALENDARS fences to named calendars; series changes ask a person through MCP elicitation

Installation¶

npx @ni-c/caldav-mcp

Configuration¶

{
  "mcpServers": {
    "caldav": {
      "command": "npx",
      "args": ["@ni-c/caldav-mcp"],
      "env": {
        "CALDAV_URL": "https://dav.example.com",
        "CALDAV_USERNAME": "ops@example.com",
        "CALDAV_CALENDARS": "Work,Team"
      }
    }
  }
}

Set CALDAV_READ_ONLY=true to keep the server strictly read-only; writes are otherwise read-modify-write over the parsed tree guarded with If-Match from the same read.

Business Relevance¶

Exec assistants and ops teams let the agent manage meetings across standards-compliant servers.
Teams on Nextcloud or Fastmail get agent scheduling without migrating calendar stacks.
Security-conscious operators use the calendar fence to keep the agent inside named calendars.
Developers pair caldav-mcp with imap-mcp and smtp-mcp for a complete ni-c communications stack.

Integration with CorpusIQ¶

CorpusIQ knows when revenue events happen; caldav-mcp knows when people are available to act on them. A composed workflow: the agent reads the revenue calendar from CorpusIQ's Stripe data, finds open slots via caldav-mcp, and books the follow-up meeting inside the same task.

Limitations¶

Brand new listing (issue #3958, Sep 5, 2026); repo and package are days old (0 stars).
Requires a CalDAV-compatible server; proprietary calendars (Google Calendar API-only setups) are out of scope.
Write safety depends on the server honoring If-Match; a misbehaving server degrades to optimistic writes.