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MCP server for iCloud (Apple) Calendar access via CalDAV

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npx icloud-calendar-mcp

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iCloud Calendar MCP Server

A security-first MCP (Model Context Protocol) server that provides AI assistants with secure access to iCloud Calendar via CalDAV. Built with comprehensive security controls aligned with the OWASP MCP Top 10.

[!CAUTION] Never use your main Apple ID password. This server requires an app-specific password which can be revoked independently without affecting your Apple ID.

Features

MCP Tools

Tool	Description	Read-Only	Destructive
`list_calendars`	List all calendars from iCloud account	Yes	No
`get_events`	Get events within a date range from a calendar	Yes	No
`create_event`	Create a new calendar event	No	No
`update_event`	Update an existing event	No	No
`delete_event`	Delete an event by ID	No	Yes

MCP Resources

Resource	Description
`calendar://calendars`	Browse available calendars

Security Features

Credential Protection - Environment variables only, never in code or config
Input Validation - All parameters validated with SSRF protection
Rate Limiting - 60 reads/min, 20 writes/min per MCP specification
Secure Error Handling - No sensitive data leakage in error messages
OWASP MCP Top 10 Compliance - 282 security tests covering all major risks
ReDoS Protection - All regex patterns tested against catastrophic backtracking
Unicode Security - Protection against homoglyph and encoding attacks

Quick Start

Prerequisites

Java 17+ (for all installation methods)
iCloud account with app-specific password

Installation

Choose your preferred installation method:

Option 1: npm (Recommended)

npx @icloud-calendar-mcp/server

Option 2: Python (uvx)

uvx icloud-calendar-mcp

Option 3: Direct JAR

# Download from GitHub Releases
curl -LO https://github.com/icloud-calendar-mcp/icloud-calendar-mcp/releases/latest/download/icloud-calendar-mcp-3.0.0-all.jar

# Run
java -jar icloud-calendar-mcp-3.0.0-all.jar

Option 4: Build from Source

git clone https://github.com/icloud-calendar-mcp/icloud-calendar-mcp.git
cd icloud-calendar-mcp
./gradlew fatJar
java -jar build/libs/icloud-calendar-mcp-3.0.0-all.jar

Configuration

Set your iCloud credentials as environment variables:

export ICLOUD_USERNAME="your-apple-id@icloud.com"
export ICLOUD_PASSWORD="your-app-specific-password"

Security Note: Use an app-specific password, not your main Apple ID password.

Claude Desktop Integration

Add to your Claude Desktop configuration:

Platform	Config Path
macOS	`~/Library/Application Support/Claude/claude_desktop_config.json`
Linux	`~/.config/claude/claude_desktop_config.json`
Windows	`%APPDATA%\Claude\claude_desktop_config.json`

Using npm (Recommended)

{
  "mcpServers": {
    "icloud-calendar": {
      "command": "npx",
      "args": ["@icloud-calendar-mcp/server"],
      "env": {
        "ICLOUD_USERNAME": "your-apple-id@icloud.com",
        "ICLOUD_PASSWORD": "your-app-specific-password"
      }
    }
  }
}

Using uvx (Python)

{
  "mcpServers": {
    "icloud-calendar": {
      "command": "uvx",
      "args": ["icloud-calendar-mcp"],
      "env": {
        "ICLOUD_USERNAME": "your-apple-id@icloud.com",
        "ICLOUD_PASSWORD": "your-app-specific-password"
      }
    }
  }
}

Using JAR directly

{
  "mcpServers": {
    "icloud-calendar": {
      "command": "java",
      "args": ["-jar", "/path/to/icloud-calendar-mcp-3.0.0-all.jar"],
      "env": {
        "ICLOUD_USERNAME": "your-apple-id@icloud.com",
        "ICLOUD_PASSWORD": "your-app-specific-password"
      }
    }
  }
}

Usage Examples

Once configured, you can ask Claude:

"What's on my calendar this week?"
"Create a meeting with John tomorrow at 2pm"
"Show me all my calendars"
"Delete the dentist appointment on Friday"
"Move my 3pm meeting to 4pm"

Tool Parameters

list_calendars

No parameters required.

get_events

Parameter	Type	Required	Description
`calendar_id`	string	Yes	Calendar identifier
`start_date`	string	Yes	Start date (YYYY-MM-DD)
`end_date`	string	Yes	End date (YYYY-MM-DD)

create_event

Parameter	Type	Required	Description
`calendar_id`	string	Yes	Target calendar
`title`	string	Yes	Event title
`start_time`	string	Cond.	ISO 8601 datetime (required for timed events)
`end_time`	string	Cond.	ISO 8601 datetime (required for timed events)
`start_date`	string	Cond.	Start date YYYY-MM-DD (required for all-day events)
`end_date`	string	Cond.	End date YYYY-MM-DD, inclusive (required for all-day events)
`is_all_day`	boolean	No	All-day event flag
`description`	string	No	Event description
`location`	string	No	Event location
`timezone`	string	No	IANA timezone (e.g., `America/New_York`)
`rrule`	string	No	Recurrence rule (e.g., `FREQ=WEEKLY;BYDAY=MO`)

update_event

Parameter	Type	Required	Description
`event_id`	string	Yes	Event UID to update
`title`	string	No	New title
`start_time`	string	No	New start time (ISO 8601)
`end_time`	string	No	New end time (ISO 8601)
`start_date`	string	No	New start date for all-day events (YYYY-MM-DD)
`end_date`	string	No	New end date for all-day events (YYYY-MM-DD)
`is_all_day`	boolean	No	Change to all-day event
`description`	string	No	New description
`location`	string	No	New location
`timezone`	string	No	IANA timezone (e.g., `America/New_York`)
`rrule`	string	No	Recurrence rule (e.g., `FREQ=WEEKLY;BYDAY=MO`)

delete_event

Parameter	Type	Required	Description
`event_id`	string	Yes	Event to delete

Security

This server is designed with security as a primary concern, following the OWASP MCP Top 10 guidelines.

Security Controls

Control	Implementation
Credential Storage	Environment variables only, never logged or exposed
Input Validation	All inputs validated (calendar IDs, dates, times, text fields)
SSRF Protection	Blocks internal IPs, localhost, and dangerous URI schemes
Rate Limiting	Sliding window: 60 reads/min, 20 writes/min
Error Handling	Passwords, tokens, paths, emails sanitized from errors
Injection Prevention	ICS content properly escaped, command injection tested
ETag Normalization	RFC 7232 compliant, strips quotes/W/ prefix/XML entities
Content-Length Guard	Early rejection of oversized responses before buffering
Circuit Breaker	Prevents cascading failures with automatic recovery
Audit Logging	CUD operations logged via MCP logging protocol (MCP08)
ReDoS Protection	All regex patterns tested for catastrophic backtracking
Unicode Security	Homoglyph, normalization, and encoding bypass protection

OWASP MCP Top 10 Coverage

Risk	Mitigation	Tests
MCP01: Token Mismanagement	Credentials masked in logs/errors, secure storage	14
MCP02: Privilege Escalation	Fixed tool set, no dynamic registration	5
MCP03: Tool Argument Injection	Input validation, parameterized operations	8
MCP04: Sensitive Data Exposure	Error sanitization, credential masking	10
MCP05: Command Injection	Input treated as data, not executed	3
MCP06: Prompt Injection	Malicious text stored as data, not interpreted	3
MCP08: Insecure Logging	Rate limiting, sensitive data sanitization	31
MCP09: Resource Exhaustion	Rate limiting, input size limits, DoS protection	25
MCP10: Context Over-sharing	Isolated state, no cross-request data leakage	3

See SECURITY.md for full security documentation and vulnerability disclosure process.

Testing

The server includes 768 comprehensive tests across 30 test suites:

./gradlew test

Test Coverage

Category	Tests	Description
Security	282	Adversarial inputs, OWASP MCP Top 10, ReDoS, Unicode
CalDAV Protocol	177	XML parsing, HTTP client, models, ETag normalization
ICS Format	98	RFC 5545 parsing, building, patching
Error Handling	56	Secure error responses, credential sanitization
Integration	40	End-to-end tools, MCP spec compliance, annotations
Input Validation	39	All parameter validation rules
Service Layer	26	Calendar operations, caching
Rate Limiting	15	Concurrent access, window reset
Cancellation	12	Operation cancellation, cleanup
Logging	9	MCP logging compliance
Progress	9	Progress reporting
E2E	5	Live CalDAV + end-to-end integration

Security Test Categories

Category	Tests	Coverage
Adversarial Inputs	53	SQL/NoSQL injection, XSS, path traversal
ICS Patcher Security	43	CRLF injection, property injection, encoding attacks
Unicode Security	38	Homoglyphs, normalization, RTL override
Logger Security	31	Log injection, credential sanitization
OWASP MCP Risks	29	MCP01-10 specific attack vectors
Progress Security	27	Token enumeration, injection
ReDoS Protection	25	Catastrophic backtracking, resource exhaustion
Cancellation Security	22	Replay attacks, race conditions
Credential Security	14	Token masking, secure storage

Running Specific Tests

# All tests
./gradlew test

# Security tests only
./gradlew test --tests "*SecurityTest*"
./gradlew test --tests "AdversarialTest"

# OWASP MCP specific tests
./gradlew test --tests "OwaspMcpSecurityTest"

# Unicode security tests
./gradlew test --tests "UnicodeSecurityTest"

# ReDoS protection tests
./gradlew test --tests "ReDoSSecurityTest"

# CalDAV tests
./gradlew test --tests "*CalDav*"

# ICS tests
./gradlew test --tests "*Ics*"

Architecture

+------------------------------------------------------------------+
|                    MCP Server (STDIO Transport)                    |
|                                                                    |
|  +----------------+  +----------------+  +----------------------+  |
|  | Rate Limiter   |  |   Input        |  |  Secure Error        |  |
|  | 60r/20w/min    |  |  Validator     |  |  Handler             |  |
|  +----------------+  +----------------+  +----------------------+  |
|                                                                    |
|  +----------------+  +----------------+  +----------------------+  |
|  | MCP Logger     |  | Cancellation   |  |  Progress            |  |
|  | (RFC 5424)     |  | Manager        |  |  Reporter            |  |
|  +----------------+  +----------------+  +----------------------+  |
|                                                                    |
|  Tools: list_calendars | get_events | create_event |               |
|         update_event | delete_event                                |
|                                                                    |
|  Resources: calendar://calendars                                   |
+------------------------------------------------------------------+
                              |
                              v
+------------------------------------------------------------------+
|                      CalendarService                               |
|  Orchestrates CalDAV operations, caches calendar metadata          |
+------------------------------------------------------------------+
                              |
                              v
+------------------------------------------------------------------+
|                      CalDAV Client Layer                           |
|                                                                    |
|  +-------------------+  +-------------------+  +----------------+  |
|  | OkHttpCalDav      |  |  IcsParser        |  |  IcsBuilder    |  |
|  | Client            |  |  (ical4j)         |  |  (RFC 5545)    |  |
|  +-------------------+  +-------------------+  +----------------+  |
|                                                                    |
|  +-------------------+  +-------------------+  +----------------+  |
|  | ICloudXml         |  |  IcsPatcher       |  |  EtagUtils     |  |
|  | Parser            |  |  (event edits)    |  |  (RFC 7232)    |  |
|  +-------------------+  +-------------------+  +----------------+  |
|                                                                    |
|  +-------------------+                                             |
|  | Credential        |                                             |
|  | Manager           |                                             |
|  +-------------------+                                             |
+------------------------------------------------------------------+
                              |
                              v
+------------------------------------------------------------------+
|                    iCloud CalDAV API                               |
|                    caldav.icloud.com                               |
+------------------------------------------------------------------+

Development

Build

# Build
./gradlew build

# Build fat JAR
./gradlew fatJar

# Run tests
./gradlew test

# Clean build
./gradlew clean build

Project Structure

src/main/kotlin/org/onekash/mcp/calendar/
├── Main.kt                 # MCP server entry point
├── caldav/                 # CalDAV protocol implementation
│   ├── CalDavClient.kt     # Client interface
│   ├── CalDavModels.kt     # Domain models
│   ├── OkHttpCalDavClient.kt
│   ├── ICloudXmlParser.kt
│   └── EtagUtils.kt        # RFC 7232 ETag normalization
├── ics/                    # ICS format handling
│   ├── IcsParser.kt        # Parse iCalendar data
│   ├── IcsBuilder.kt       # Generate iCalendar data
│   └── IcsPatcher.kt       # Patch existing events (CRLF-safe)
├── service/                # Business logic
│   ├── CalendarService.kt
│   └── EventCache.kt
├── security/               # Security controls
│   └── CredentialManager.kt
├── validation/             # Input validation
│   └── InputValidator.kt
├── error/                  # Error handling
│   └── SecureErrorHandler.kt
├── ratelimit/              # Rate limiting
│   └── RateLimiter.kt
├── logging/                # MCP logging
│   └── McpLogger.kt
├── progress/               # Progress reporting
│   └── ProgressReporter.kt
└── cancellation/           # Operation cancellation
    └── CancellationManager.kt

Testing with MCP Inspector

ICLOUD_USERNAME="test@icloud.com" \
ICLOUD_PASSWORD="test-app-password" \
npx @mcp-use/inspector java -jar build/libs/icloud-calendar-mcp-3.0.0-all.jar

Contributing

We welcome contributions! Please see CONTRIBUTING.md for guidelines.

Security Issues

For security vulnerabilities, please see SECURITY.md for our responsible disclosure process. Do not open public issues for security vulnerabilities.

License

This project is licensed under the Apache License 2.0 - see the LICENSE file for details.

Acknowledgments

Model Context Protocol by Anthropic
MCP Kotlin SDK by Anthropic & JetBrains
ical4j for ICS parsing
OkHttp for HTTP client
OWASP MCP Top 10 for security guidance

server

Installation

Reviews

Documentation

iCloud Calendar MCP Server

Features

MCP Tools

MCP Resources

Security Features

Quick Start

Prerequisites

Installation

Option 1: npm (Recommended)

Option 2: Python (uvx)

Option 3: Direct JAR

Option 4: Build from Source

Configuration

Claude Desktop Integration

Usage Examples

Tool Parameters

list_calendars

get_events

create_event

update_event

delete_event

Security

Security Controls

OWASP MCP Top 10 Coverage

Testing

Test Coverage

Security Test Categories

Running Specific Tests

Architecture

Development

Build

Project Structure

Testing with MCP Inspector

Contributing

Security Issues

License

Acknowledgments

Tags

Security Checklist