Immutable server definition.

A %FastestMCP.Server{} is the declarative description of everything the runtime should expose:

• tools
• resources
• resource templates
• prompts
• middleware
• transforms
• providers
• auth configuration
• dependency resolvers
• extra HTTP routes

This module is intentionally pure. Every builder returns a new struct instead of mutating a running process. The runtime only starts later, through FastestMCP.start_server/2 or FastestMCP.ServerModule.

Typical Flow

Most code builds a server in a pipeline:

server =
  FastestMCP.Server.new("docs")
  |> FastestMCP.Server.add_tool("sum", fn %{"a" => a, "b" => b}, _ctx -> a + b end)
  |> FastestMCP.Server.add_dependency(:repo, fn -> MyApp.Repo end)

The same shape is usually reached through the facade:

server =
  FastestMCP.server("docs")
  |> FastestMCP.add_tool("sum", fn %{"a" => a, "b" => b}, _ctx -> a + b end)

Relationship To The Runtime

FastestMCP.Server is the build-time object.

The server runtime is the running process tree built from that object. That split is deliberate: the public builder stays simple, testable, and easy to compose, while runtime concerns stay inside OTP processes.

Duplicate Registration Policy

on_duplicate: controls what happens when the same local component name or URI is registered twice in the same server definition:

• :error - raise immediately
• :warn - log a warning and replace the existing definition
• :ignore - keep the existing definition
• :replace - replace the existing definition silently

This policy only applies to the local server definition. Provider precedence and mount ordering remain separate runtime concerns.