rstime Plugin

January 23, 2026 ยท View on GitHub

A Model Context Protocol (MCP) plugin for working with time and timezone information. The rstime plugin provides tools for retrieving the current time in different timezones and parsing RFC2822 formatted time strings.

Overview

The rstime plugin is a WebAssembly-based MCP plugin written in Rust that exposes time-related functionality through the Model Context Protocol. It allows LLM clients to:

  • Get the current time in any timezone
  • Parse RFC2822 formatted time strings to Unix timestamps
  • Complete timezone names for better user experience

Features

Tools

get_time

Returns the current time in a specified timezone.

Input:

  • timezone (optional, string): The timezone identifier (e.g., America/New_York, Europe/London, Asia/Tokyo). Defaults to UTC if not provided.

Output:

  • current_time (string): The current time in RFC2822 format for the specified timezone.

Example:

Tool: get_time
Input: {"timezone": "America/Los_Angeles"}
Output: "Tue, 15 Jan 2024 10:30:45 -0800"

parse_time

Parses an RFC2822 formatted time string and returns the corresponding Unix timestamp.

Input:

  • time (required, string): The time string in RFC2822 format to parse.

Output:

  • timestamp (integer): The parsed timestamp in seconds since the Unix epoch.

Example:

Tool: parse_time
Input: {"time": "Tue, 15 Jan 2024 18:30:45 +0000"}
Output: 1705344645

Prompts

get_time_with_timezone

A prompt that guides the user to get the current time for a specific timezone.

Arguments:

  • timezone (optional, string): The timezone to retrieve time information for. Defaults to UTC.

Response: Returns an assistant message suggesting to get the time for the specified timezone.

Building

Prerequisites

  • Rust 1.70 or later
  • Extism toolchain for WASM compilation

Build Steps

# Build the WebAssembly plugin
cargo build --release --target wasm32-wasip1

# The compiled WASM file will be available at target/wasm32-wasip1/release/plugin.wasm

Alternatively, you can use the provided prepare.sh script:

./prepare.sh

This will create the compiled rstime.wasm file.

Docker Support

A Dockerfile is included for containerized deployment. Build it with:

docker build -t rstime:latest .

Testing

The plugin includes comprehensive test coverage. Run tests with, changing the target to your architecture:

cargo test --lib --target x86_64-apple-darwin

Test Coverage

The test suite covers:

  • Getting time in UTC and various timezones
  • Handling invalid timezone names
  • Parsing valid and invalid RFC2822 time strings
  • Tool listing and metadata
  • Prompt retrieval and listing
  • Resource operations
  • Error handling and edge cases

Supported Timezones

The plugin supports all timezones from the IANA timezone database through the chrono-tz crate. Some common examples include:

  • UTC - Coordinated Universal Time
  • America/New_York - Eastern Time
  • America/Chicago - Central Time
  • America/Denver - Mountain Time
  • America/Los_Angeles - Pacific Time
  • Europe/London - Greenwich Mean Time
  • Europe/Paris - Central European Time
  • Asia/Tokyo - Japan Standard Time
  • Asia/Shanghai - China Standard Time
  • Australia/Sydney - Australian Eastern Time

For a complete list, refer to the IANA timezone database.

Dependencies

  • chrono - Date and time handling
  • chrono-tz - Timezone support
  • extism-pdk - Extism Plugin Development Kit for MCP
  • serde - Serialization/deserialization
  • serde_json - JSON handling
  • anyhow - Error handling
  • base64 - Base64 encoding/decoding

Usage Example

When integrated with an MCP-compatible client, you can use the plugin like this:

User: What time is it in Tokyo?

Client calls: get_time tool with {"timezone": "Asia/Tokyo"}
Plugin returns: Current time in RFC2822 format for Asia/Tokyo

Client: The current time in Tokyo is [result]

Architecture

The plugin follows the Extism PDK architecture:

  • lib.rs: Main plugin implementation with tool and prompt logic
  • pdk: PDK-specific types and exported functions for MCP communication
  • Cargo.toml: Rust dependencies and build configuration

The plugin compiles to WebAssembly and implements the MCP protocol through Extism's foreign function interface.

Error Handling

The plugin gracefully handles common errors:

  • Invalid timezone: Returns a descriptive error message
  • Missing required arguments: Provides helpful feedback about required parameters
  • Invalid time format: Reports parsing errors with context
  • Unknown tools/prompts: Returns appropriate error responses

Contributing

When contributing to this plugin:

  1. Maintain the existing code style
  2. Add tests for new functionality
  3. Update this README with any new features
  4. Ensure all tests pass before submitting

License

This plugin is part of the hyper-mcp project. See the main project repository for license information.