Components

What is a Component?

An ACT component is a WebAssembly module that exports the act-world world:

world act-world {
    export act:core/tool-provider;
}

It’s a single .wasm file containing:

• Tool implementations
• JSON Schemas for all tool arguments
• Localized descriptions and documentation
• Component metadata (name, version, author)

Component Info

Component metadata lives in a WASM custom section named act:component, encoded as dCBOR (RFC 8949). This allows tools like act info to inspect a component without instantiating it.

$ act info my-component.wasm
Name:        my-component
Version:     0.1.0
Description: A useful set of tools
Tools:       3

Tool Definitions

Each tool declares:

Field	Type	Purpose
name	string	Machine-readable identifier
description	localized-string	Human/agent-readable description
input-schema	JSON Schema	Argument validation schema
annotations	map	Hints like std:read-only, std:destructive
usage-hints	list	When to use this tool
anti-usage-hints	list	When NOT to use this tool
examples	list	Example invocations

Localized Strings

Descriptions use the localized-string variant:

// Simple — single language
localized_string::plain("Encode text as base64")

// Localized — multiple languages (BCP 47)
localized_string::localized(vec![
    ("en", "Encode text as base64"),
    ("ru", "Закодировать текст в base64"),
])

Component Types

Clients (Static Tools)

Fixed set of known tools. Examples:

• component-http-client — HTTP fetch
• component-sqlite — SQL database access
• component-filesystem — file operations

Bridges (Dynamic Tools)

Generate tools at runtime from external specs. The tool set depends on the connected service:

• component-openapi-bridge — tools from an OpenAPI spec
• component-mcp-bridge — tools from an MCP server
• component-act-http-bridge — tools from a remote ACT component

Language Support

Language	Path	Streaming
Rust	Native wasip3	Full async + stream
Python	componentize-py	Async func (wasip3)
JS/TS	jco / componentize-js	Limited (no streams)
Go	TinyGo	Cooperative (wasip2 shim)
C/C++	wasi-sdk	Via wasip2 shim

Distribution

A .wasm file is the package. No archive formats needed — schemas, docs, and assets are embedded in the binary.

# Run a component from the registry
act run dev.actcore:component-sqlite@0.1.0

# Cached at ~/.cache/actcore/