Hermes MCP

What is Hermes MCP?

Hermes MCP is a high-performance Elixir SDK for the Model Context Protocol (MCP). It provides a feature‑complete client implementation conforming to the MCP 2024‑11‑05 specification and is available both as a Hex package and a standalone CLI binary. The library targets Elixir developers who need to interact with MCP servers from Elixir applications or test MCP servers interactively.

How to use Hermes MCP?

Add {:hermes_mcp, "~> 0.5"} to your mix.exs dependencies, or download the CLI binary from the GitHub releases page and run it with transport arguments (e.g. --transport sse --base-url="http://localhost:8000"). To set up a client, start a Hermes.Client process before its associated transport process, then use functions like Hermes.Client.call_tool/3 to make requests.

Key features of Hermes MCP

• Complete MCP client implementation (2024‑11‑05)
• Multiple transport options: STDIO, HTTP/SSE, and WebSocket
• Built‑in connection supervision and automatic recovery
• Comprehensive capability negotiation
• Progress tracking and cancellation support
• Structured logging system

Use cases of Hermes MCP

• Interactively test MCP servers via CLI or Mix tasks
• Integrate MCP client capabilities into an Elixir application
• Automate tool, resource, and prompt exploration from Elixir
• Build robust MCP‑based workflows with automatic recovery

FAQ from Hermes MCP

Is Hermes MCP stable?

The library is under active development and may expect breaking changes. It provides a feature‑complete client for the MCP 2024‑11‑05 specification.

Which platforms and Elixir versions are supported?

Hermes MCP runs on any platform supported by the Erlang VM. The CLI binary is available for Linux and macOS (Intel and ARM). The library requires Elixir and can be added as a dependency in a standard mix project.

Does Hermes MCP support server implementations?

Currently Hermes MCP offers only the client. Server‑side components (STDIO, HTTP/SSE, Streamable HTTP transport) are planned for future releases.

Which MCP transports are supported?

The client supports STDIO, HTTP/SSE, and WebSocket transports.

What is the license?

Hermes MCP is released under the MIT License.