MCP Server Documentation

Give your AI agents a calendar brain with the Model Context Protocol server

What is MCP?

The Model Context Protocol (MCP) allows AI assistants like Claude to access external tools and data sources. The rrule.net MCP server gives AI agents deterministic, explainable scheduling capabilities.

🎉 Free Tier Available

The rrule.net MCP server is currently free and authless (no API token required). Rate limit: 100 requests per 24 hours per IP.

Configuration for Claude Desktop

Method 1: Via Settings UI (Recommended)

  1. Open Claude Desktop
  2. Go to Settings → Connectors
  3. Click "Add custom connector"
  4. Enter URL: https://mcp.rrule.net
  5. Click "Add"

Note: This method requires Claude Desktop Pro, Max, Team, or Enterprise plan.

Method 2: Via Configuration File

Add this to your Claude Desktop configuration file (~/Library/Application Support/Claude/claude_desktop_config.json on macOS): 

{
  "mcpServers": {
    "rrule-net-free": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://mcp.rrule.net"
      ]
    }
  }
}

After updating the configuration, restart Claude Desktop completely (Cmd+Q then relaunch).

Available Tools

The free tier provides 3 read-only tools for schedule validation, simulation, and explanation.

validate_schedule

Validate and normalize a scheduling rule from natural language, cron, or RRule format

Input:

  • input: Schedule rule (e.g., "Every Monday at 9am", "0 9 * * 1", "FREQ=DAILY;BYHOUR=9")
  • timezone: IANA timezone identifier (e.g., "Europe/Paris", "America/New_York")
  • language: Optional language for explanation ("en" or "fr")

Returns: Normalized RRule, explanation, confidence score, next occurrence

simulate_schedule

Simulate future occurrences of a schedule rule with timezone-aware DST handling

Input:

  • rrule: Object with dtstart (ISO 8601 UTC) and rule (RRule string)
  • timezone: IANA timezone identifier for interpretation
  • count: Number of occurrences to simulate (1-100, default: 10)

Returns: List of ISO 8601 UTC timestamps, automatically handles DST transitions

describe_schedule

Get a human-readable explanation of a schedule rule in natural language

Input:

  • rrule: Object with dtstart and rule
  • timezone: IANA timezone identifier
  • language: Optional language for explanation ("en" or "fr")

Returns: Human-readable explanation with confidence score

Example Usage

User prompt to Claude:

"Valide la règle 'Every first Monday of the month at 10am' avec timezone America/New_York, et simule les 12 prochaines occurrences"

Claude uses MCP tools to:

  1. Call validate_schedule with the natural language input
  2. Receive normalized RRule: FREQ=MONTHLY;BYDAY=+1MO;BYHOUR=10;BYMINUTE=0;BYSECOND=0
  3. Call simulate_schedule with the normalized RRule
  4. Return 12 occurrences with automatic DST handling (EST/EDT transitions)

Other example prompts:

  • "Normalise cette expression cron : 0 9 * * 1"
  • "Montre-moi les 5 prochaines dates pour la règle FREQ=WEEKLY;BYDAY=MO;BYHOUR=9"
  • "Explique-moi en français cette règle : FREQ=MONTHLY;BYMONTHDAY=1;BYHOUR=9"
  • "Est-ce que '0 */4 * * *' est une règle valide ?"

MCP server endpoint: https://mcp.rrule.net