Feature Flags

Neva uses Cargo feature flags to keep compile times low and binary size minimal — only the code you actually need gets compiled. This page explains all available features and how to combine them for common scenarios.

Quick Start

For most projects, the bundled presets are all you need:

[dependencies]
# Full-featured MCP server
neva = { version = "...", features = ["server-full"] }

# Full-featured MCP client
neva = { version = "...", features = ["client-full"] }

# Both server and client
neva = { version = "...", features = ["full"] }

Feature Reference

Presets

Feature	Includes	Description
full	server-full + client-full	Everything — for apps that run both a server and a client
server-full	server-macros, tracing, http-server-volga, server-tls, di, tasks	All server capabilities, including the default Volga-based HTTP server
client-full	client-macros, tracing, http-client, client-tls, tasks	All client capabilities

Server Features

Feature	Includes	Description
server	—	Core server runtime: tool, resource, and prompt handler registration, stdio transport
server-macros	server, macros	Adds attribute macros (#[tool], #[resource], #[prompt], etc.)
http-server	server	Engine-agnostic Streamable HTTP abstractions — pulls in no HTTP framework. Plug in your own stack (axum, hyper, actix-web, …) by implementing HttpEngine
http-server-volga	http-server	Default Volga-based HTTP server adapter, including JWT auth
server-tls	http-server-volga	TLS support for the default HTTP server, including automatic dev certificate generation

Client Features

Feature	Includes	Description
client	—	Core client runtime: tool calls, resource reads, prompt fetching, stdio transport
client-macros	client, macros	Adds attribute macros (#[sampling], #[elicitation])
http-client	client	Streamable HTTP transport and SSE stream support
client-tls	—	TLS support for the HTTP client (rustls)

Shared Features

Feature	Description
macros	Procedural macro infrastructure (shared between server-macros and client-macros)
di	Dependency injection — service container with singleton, scoped, and transient lifetimes
tasks	Task-augmented requests — long-running async tool execution with polling
tracing	Structured logging via the tracing ecosystem and MCP log notifications

Common Configurations

Minimal stdio server (no macros)

neva = { version = "...", features = ["server"] }

Use this when you prefer to register handlers manually with map_tool(), map_resource(), and map_prompt() instead of attribute macros.

Server with macros, without HTTP

neva = { version = "...", features = ["server-macros", "tracing"] }

Attribute macros and logging, but no HTTP transport compiled in. Useful for stdio-only servers.

HTTP server without TLS

neva = { version = "...", features = ["server-macros", "http-server-volga", "tracing", "di", "tasks"] }

Default (Volga-based) HTTP transport without TLS — suitable for local or internal deployments behind a reverse proxy.

HTTP server on a custom stack (axum / hyper / actix-web)

neva = { version = "...", features = ["server-macros", "http-server", "tracing", "di", "tasks"] }
# plus your framework of choice
axum = "0.8"

The http-server feature ships the engine-agnostic abstractions only — no Volga, no framework dependency. You implement HttpEngine for your stack and wire it in via HttpServer::from_engine(...). See Custom HTTP Stack for a complete walk-through.

Breaking change in v0.3.3

Before v0.3.3, the http-server flag transitively pulled in Volga. Starting with v0.3.3, http-server is engine-agnostic and contains no framework. If you depend on the bundled Volga server, switch to http-server-volga (or stay on server-full, which now selects http-server-volga for you).

Minimal HTTP client

neva = { version = "...", features = ["http-client"] }

A lightweight client that connects to remote MCP servers over HTTP, without macros or tracing.

Server + embedded client (agent pattern)

neva = { version = "...", features = ["server-full", "http-client"] }

An MCP server that also acts as a client — for example, a server that delegates sampling requests or fans out to other MCP servers.

Feature Composition

The diagram below shows how features build on each other:

full
├── server-full
│   ├── server-macros
│   │   ├── server
│   │   └── macros
│   ├── http-server-volga
│   │   └── http-server
│   │       └── server
│   ├── server-tls
│   │   └── http-server-volga
│   ├── tracing
│   ├── di
│   └── tasks
└── client-full
    ├── client-macros
    │   ├── client
    │   └── macros
    ├── http-client
    │   └── client
    ├── client-tls
    ├── tracing
    └── tasks