clock-mcp

A Model Context Protocol server that gives an AI assistant a wall clock. It exposes five tools for reading the current time, doing duration math, and converting between IANA timezones, over MCP's stdio transport. Single Rust binary.

Install

cargo install clock-mcp

This installs the clock-mcp binary to ~/.cargo/bin/, which is on your PATH if you have a normal Rust setup.

Or build from source:

git clone https://github.com/devrelopers/clock-mcp.git
cd clock-mcp
cargo install --path .

Use it

With Claude Desktop

Add a clock entry to your claude_desktop_config.json:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json
• Linux: ~/.config/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "clock": {
      "command": "clock-mcp"
    }
  }
}

If you already have other servers in mcpServers, merge the clock entry alongside them rather than replacing the block.

Restart Claude Desktop. The five tools below will appear in the tools picker.

With Claude Code

claude mcp add clock clock-mcp

Verify with claude mcp list.

Tool reference

now

Returns the current wall-clock time.

Params

Name	Type	Required	Description
timezone	string (IANA)	no	e.g. "America/Denver". Defaults to "UTC".

Example response

{
  "iso8601": "2026-04-20T12:03:26.639756-06:00",
  "unix_seconds": 1776708206,
  "timezone": "America/Denver"
}

time_until

Returns the duration from now until a target datetime. Negative if the target is already in the past.

Params

Name	Type	Required	Description
target	string (ISO 8601 / RFC 3339)	yes	e.g. "2026-12-31T23:59:59Z".

Example response

{
  "from": "2026-04-20T18:03:26.649537+00:00",
  "to": "2026-12-31T23:59:59+00:00",
  "duration": {
    "total_seconds": 22053392,
    "days": 255,
    "hours": 5,
    "minutes": 56,
    "seconds": 32,
    "human": "255d 5h 56m 32s"
  }
}

time_since

Returns the duration from a past datetime until now. Negative if the input is actually in the future.

Params

Name	Type	Required	Description
past	string (ISO 8601 / RFC 3339)	yes	e.g. "2026-01-01T00:00:00Z".

Example response

{
  "from": "2026-01-01T00:00:00+00:00",
  "to": "2026-04-20T18:03:26.659573+00:00",
  "duration": {
    "total_seconds": 9482606,
    "days": 109,
    "hours": 18,
    "minutes": 3,
    "seconds": 26,
    "human": "109d 18h 3m 26s"
  }
}

time_between

Returns the duration between two datetimes. Negative if end precedes start.

Params

Name	Type	Required	Description
start	string (ISO 8601 / RFC 3339)	yes	Start datetime.
end	string (ISO 8601 / RFC 3339)	yes	End datetime.

Example response

{
  "from": "2026-01-01T00:00:00+00:00",
  "to": "2026-01-02T01:30:00+00:00",
  "duration": {
    "total_seconds": 91800,
    "days": 1,
    "hours": 1,
    "minutes": 30,
    "seconds": 0,
    "human": "1d 1h 30m"
  }
}

convert_timezone

Re-expresses an instant in another IANA timezone. The unix_seconds field is preserved across the conversion — only the wall-clock representation changes.

Params

Name	Type	Required	Description
datetime	string (ISO 8601 / RFC 3339)	yes	Input datetime with a timezone offset.
target_timezone	string (IANA)	yes	e.g. "Asia/Tokyo".

Example response

{
  "original": "2026-04-20T21:00:00+00:00",
  "converted": "2026-04-21T06:00:00+09:00",
  "target_timezone": "Asia/Tokyo",
  "unix_seconds": 1776718800
}

Error shape

Every tool returns a structured JSON error (never a panic) on bad input. The payload has a required error string and an optional hint:

{
  "error": "Unknown timezone: \"Narnia/Cair_Paravel\"",
  "hint": "Use an IANA timezone name like 'America/Denver', 'Europe/Berlin', 'Asia/Tokyo', or 'UTC'."
}

The MCP envelope around these errors sets isError: true on the tools/call result.

Development

cargo build --release      # build the binary
cargo test                 # run unit tests
cargo clippy -- -D warnings
cargo fmt

Poke it by hand

The server speaks MCP over stdio. You can talk to it with any MCP client, including the reference inspector:

npx @modelcontextprotocol/inspector clock-mcp

Or drive a raw JSON-RPC handshake yourself:

printf '%s\n%s\n' \
  '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"probe","version":"0"}}}' \
  '{"jsonrpc":"2.0","id":2,"method":"tools/list"}' \
  | clock-mcp

License

MIT. See LICENSE.