@arcturn/types

Shared type contracts for the Arcturn agent harness. This package ships type declarations only — no runtime code, no dependencies. Every other Arcturn package (and any SDK consumer) imports these types instead of redefining them.

What's in it

src/index.ts re-exports everything from:

• ai.js — provider-facing message/content types used by the LLM client.
• events.js — the AgentEvent union the agent loop streams.
• mcp.js — Model Context Protocol wire types.
• messages.js — Message, tool call/result content, and related shapes.
• models.js — ModelSpec, ModelCapabilities, ProviderId.
• permissions.js — permission rule and decision types.
• protocol.js — types shared with @arcturn/protocol's wire format, including PROTOCOL_VERSION.
• session.js — SessionStore and session-tree types.
• tools.js — the Tool, ToolDefinition, ToolExecutionContext, and ToolResult interfaces every tool implements.

Install

Arcturn is not yet published to npm. Until it is, use it from a clone of the monorepo as a pnpm workspace package:

git clone https://github.com/sitharaj88/arcturn.git && cd arcturn
pnpm install && pnpm -r build

Then depend on it from another workspace package: "@arcturn/types": "workspace:*".

Usage

import type { Tool, ToolExecutionContext, ToolResult } from "@arcturn/types";

const echo: Tool = {
  name: "echo",
  description: "Echo the input text back.",
  parameters: {
    type: "object",
    properties: { text: { type: "string" } },
    required: ["text"],
  },
  async execute(input: { text: string }, _ctx: ToolExecutionContext): Promise<ToolResult> {
    return { content: [{ type: "text", text: input.text }] };
  },
};

Docs

• Custom tools — the full Tool interface, worked example, and error handling.
• Embedding with the SDK — how this package fits with @arcturn/core, @arcturn/ai, @arcturn/tools, and @arcturn/mcp.

License

Apache-2.0 — see LICENSE.

👤 Author

Sitharaj Seenivasan

• 🌐 Website: sitharaj.in
• 💼 LinkedIn: sitharaj08
• 💻 GitHub: sitharaj88

☕ Support

If this project helps you, consider buying me a coffee — it keeps the work going.

📄 License

Licensed under the Apache License 2.0. © 2026 Sitharaj Seenivasan.