# Custom Tools and Toolkits (Experimental) (/docs/toolkits/custom-tools-and-toolkits)

> Custom tool APIs are experimental. TypeScript uses `experimental_createTool()` / `experimental_createToolkit()`. Python uses `@composio.experimental.tool()` / `composio.experimental.Toolkit(...)`. The session `experimental` option may change in future releases.

> Custom tools work with **native tools** (`session.tools()`). MCP support is coming soon — custom tools are not available via the MCP server URL yet.

Custom tools let you define tools that run in-process alongside remote Composio tools within a session. There are three patterns:

* **Standalone tools** — for internal app logic that doesn't need Composio auth (DB lookups, in-memory data, business rules)
* **Extension tools** — wrap a Composio toolkit's API with custom business logic via `extendsToolkit` / `extends_toolkit`, using `ctx.proxyExecute()` / `ctx.proxy_execute()` for authenticated requests
* **Custom toolkits** — group related standalone tools under a namespace

The example below defines one of each and binds them to a session:

**TypeScript:**

```typescript
import { Composio, experimental_createTool, experimental_createToolkit } from "@composio/core";
import { z } from "zod/v3";

// ── Standalone tool ─────────────────────────────────────────────
// Internal data lookup — no Composio auth needed.
// ctx.userId identifies which user's session is running.
const profiles: Record<string, { name: string; email: string; tier: string }> = {
  "user_1": { name: "Alice Johnson", email: "alice@myapp.com", tier: "enterprise" },
  "user_2": { name: "Bob Smith", email: "bob@myapp.com", tier: "free" },
};

const getUserProfile = experimental_createTool("GET_USER_PROFILE", {
  name: "Get user profile",
  description: "Retrieve the current user's profile from the internal directory",
  inputParams: z.object({}),
  execute: async (_input, ctx) => {
    const profile = profiles[ctx.userId];
    if (!profile) throw new Error(`No profile found for user "${ctx.userId}"`);
    return profile;
  },
});

// ── Extension tool ──────────────────────────────────────────────
// Wraps Gmail API with business logic. Inherits auth via extendsToolkit,
// so ctx.proxyExecute() handles credentials automatically.
const sendPromoEmail = experimental_createTool("SEND_PROMO_EMAIL", {
  name: "Send promo email",
  description: "Send the standard promotional email to a recipient",
  extendsToolkit: "gmail",
  inputParams: z.object({
    to: z.string().describe("Recipient email address"),
  }),
  execute: async (input, ctx) => {
    const subject = "You're invited to try MyApp Pro";
    const body = "Hi there,\n\nWe'd love for you to try MyApp Pro — free for 14 days.\n\nBest,\nThe MyApp Team";
    const raw = btoa(`To: ${input.to}\r\nSubject: ${subject}\r\nContent-Type: text/plain; charset=UTF-8\r\n\r\n${body}`);

    const res = await ctx.proxyExecute({
      toolkit: "gmail",
      endpoint: "https://gmail.googleapis.com/gmail/v1/users/me/messages/send",
      method: "POST",
      body: { raw },
    });
    return { status: res.status, to: input.to };
  },
});

// ── Custom toolkit ──────────────────────────────────────────────
// Groups standalone tools that don't need Composio auth under a toolkit.
// Tools inside a toolkit cannot use extendsToolkit.
const userManagement = experimental_createToolkit("USER_MANAGEMENT", {
  name: "User management",
  description: "Manage user roles and permissions",
  tools: [
    experimental_createTool("ASSIGN_ROLE", {
      name: "Assign role",
      description: "Assign a role to a user in the internal system",
      inputParams: z.object({
        user_id: z.string().describe("Target user ID"),
        role: z.enum(["admin", "editor", "viewer"]).describe("Role to assign"),
      }),
      execute: async ({ user_id, role }) => ({ user_id, role, assigned: true }),
    }),
  ],
});

// ── Bind to session ─────────────────────────────────────────────
// Pass custom tools and toolkits via the experimental option.
// session.tools() returns both remote Composio tools and your custom tools.
const composio = new Composio({ apiKey: "your_api_key" });

const session = await composio.create("user_1", {
  toolkits: ["gmail"],
  experimental: {
    customTools: [getUserProfile, sendPromoEmail],
    customToolkits: [userManagement],
  },
});

const tools = await session.tools();
```

**Python:**

```python
import base64

from pydantic import BaseModel, Field

from composio import Composio

composio = Composio(api_key="your_api_key")

class UserLookupInput(BaseModel):
    user_id: str = Field(description="User ID")

USERS = {
    "user_1": {"name": "Alice Johnson", "email": "alice@myapp.com", "tier": "enterprise"},
    "user_2": {"name": "Bob Smith", "email": "bob@myapp.com", "tier": "free"},
}

@composio.experimental.tool()
def get_user_profile(input: UserLookupInput, ctx):
    """Retrieve the current user's profile from the internal directory."""
    profile = USERS.get(input.user_id)
    if not profile:
        raise ValueError(f'No profile found for user "{input.user_id}"')
    return profile

class PromoEmailInput(BaseModel):
    to: str = Field(description="Recipient email address")

@composio.experimental.tool(extends_toolkit="gmail")
def send_promo_email(input: PromoEmailInput, ctx):
    """Send the standard promotional email to a recipient."""
    subject = "You're invited to try MyApp Pro"
    body = (
        "Hi there,\n\n"
        "We'd love for you to try MyApp Pro — free for 14 days.\n\n"
        "Best,\nThe MyApp Team"
    )
    raw_msg = (
        f"To: {input.to}\r\n"
        f"Subject: {subject}\r\n"
        "Content-Type: text/plain; charset=UTF-8\r\n\r\n"
        f"{body}"
    )
    raw = base64.urlsafe_b64encode(raw_msg.encode()).decode().rstrip("=")

    res = ctx.proxy_execute(
        toolkit="gmail",
        endpoint="https://gmail.googleapis.com/gmail/v1/users/me/messages/send",
        method="POST",
        body={"raw": raw},
    )
    return {"status": res.status, "to": input.to}

user_management = composio.experimental.Toolkit(
    slug="USER_MANAGEMENT",
    name="User management",
    description="Manage user roles and permissions",
)

class AssignRoleInput(BaseModel):
    user_id: str = Field(description="Target user ID")
    role: str = Field(description="Role to assign")

@user_management.tool()
def assign_role(input: AssignRoleInput, ctx):
    """Assign a role to a user in the internal system."""
    return {"user_id": input.user_id, "role": input.role, "assigned": True}

session = composio.create(
    user_id="user_1",
    toolkits=["gmail"],
    experimental={
        "custom_tools": [get_user_profile, send_promo_email],
        "custom_toolkits": [user_management],
    },
)

tools = session.tools()
```

# How custom tools work with meta tools

Custom tools integrate seamlessly with Composio's meta tools:

* **`COMPOSIO_SEARCH_TOOLS`** automatically includes your custom tools and toolkits in search results, giving slight priority to tools that don't require auth or are already connected
* **`COMPOSIO_GET_TOOL_SCHEMAS`** returns schemas for custom tools alongside remote tools — the agent sees them as first-class tools
* **`COMPOSIO_MULTI_EXECUTE_TOOL`** intelligently splits execution — custom tools run in-process while remote tools go to the backend, results are merged transparently
* **`COMPOSIO_MANAGE_CONNECTIONS`** handles auth for extension tools — if a tool extends `gmail`, the agent can prompt the user to connect Gmail just like any other toolkit
* Custom tools are **not supported in Workbench** — the LLM is made aware of this and will not attempt to use them there

# Best practices

* **Descriptive names and slugs** — The agent sees your tool's name and description to decide when to use it. Be specific: "Send weekly promo email" is better than "Send email". In TypeScript, define uppercase slugs like `SEND_PROMO_EMAIL`. In Python, inferred slugs come from the function name, so `snake_case` function names produce the cleanest defaults; or pass `slug=` / `name=` explicitly.
* **Detailed descriptions** — Include what the tool does, when to use it, and what it returns. The agent relies on this to pick the right tool.
* **Use `extendsToolkit` / `extends_toolkit` for auth** — If your tool needs Gmail/GitHub/etc. auth for `ctx.proxyExecute()` / `ctx.proxy_execute()` or `ctx.execute()`, set the toolkit extension so connection management is handled seamlessly via `COMPOSIO_MANAGE_CONNECTIONS`.
* **In Python, annotations are the schema** — The first parameter must be a Pydantic `BaseModel`, and its field descriptions become the input schema. Docstrings are used as the default tool description unless you pass `description=`.
* **Tool names get prefixed** — Slugs exposed to the agent are automatically prefixed with `LOCAL_` and the toolkit name (if any). `GET_USER_PROFILE` becomes `LOCAL_GET_USER_PROFILE`, `ASSIGN_ROLE` in `USER_MANAGEMENT` becomes `LOCAL_USER_MANAGEMENT_ASSIGN_ROLE`. Your slugs cannot start with `LOCAL_` — this prefix is reserved.

For more best practices, see [How to Build Tools for AI Agents: A Field Guide](https://composio.dev/blog/how-to-build-tools-for-ai-agents-a-field-guide).

# Verifying registration

Use `session.customTools()` / `session.customToolkits()` in TypeScript or `session.custom_tools()` / `session.custom_toolkits()` in Python to list registered tools and toolkits. Registered tool slugs include their final `LOCAL_` prefix, and toolkit-scoped tools also include the toolkit slug.

Reference: [TypeScript ToolRouterSession](/reference/sdk-reference/typescript/tool-router-session) · [Python SDK Reference](/reference/sdk-reference/python)

# Programmatic execution

Use `session.execute()` to run custom tools directly, outside of an agent loop (e.g. `session.execute("GET_USER_PROFILE")`). Custom tools execute in-process; remote tools are sent to the backend automatically.

Reference: [Tool Router API Reference](/reference/api-reference/tool-router) · [TypeScript ToolRouterSession](/reference/sdk-reference/typescript/tool-router-session) · [Python SDK Reference](/reference/sdk-reference/python)

# SessionContext

Every custom tool's `execute` function receives `(input, ctx)`. The `ctx` object provides:

**TypeScript:**

| Method                        | Description                                                                                                                                                                  |
| ----------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `ctx.userId`                  | The user ID for the current session.                                                                                                                                         |
| `ctx.proxyExecute(params)`    | Authenticated HTTP request via Composio's auth layer. Params: `toolkit`, `endpoint`, `method`, `body?`, `parameters?` (array of `{ in: "query" \| "header", name, value }`). |
| `ctx.execute(toolSlug, args)` | Execute any Composio native tool from within your custom tool.                                                                                                               |

**Python:**

| Method                              | Description                                                                                                                                                                        |
| ----------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `ctx.user_id`                       | The user ID for the current session.                                                                                                                                               |
| `ctx.proxy_execute(...)`            | Authenticated HTTP request via Composio's auth layer. Params: `toolkit`, `endpoint`, `method`, `body=None`, `parameters=[{"in": "query" \| "header", "name": ..., "value": ...}]`. |
| `ctx.execute(tool_slug, arguments)` | Execute any Composio native tool from within your custom tool.                                                                                                                     |

In Python, `parameters` dictionaries accept both `in` and `type`; this guide uses `in` to match the TypeScript examples.

Reference: [TypeScript SessionContextImpl](/reference/sdk-reference/typescript/session-context-impl) · [Python SDK Reference](/reference/sdk-reference/python)

---

📚 **More documentation:** [View all docs](https://docs.composio.dev/llms.txt) | [Glossary](https://docs.composio.dev/llms.mdx/docs/glossary) | [Cookbooks](https://docs.composio.dev/llms.mdx/cookbooks) | [API Reference](https://docs.composio.dev/llms.mdx/reference)

---

# Composio SDK — Instructions for AI Code Generators

**Purpose:** Enforce only the **current** and **correct** patterns for integrating [Composio](https://composio.dev/) tools into AI agents.
**Scope:** All AI-generated code using Composio must follow these guardrails.

---

## 1. Correct Composio Integration

Composio supports two integration modes: **Native Tools** (with a provider package) and **MCP** (no provider package needed).

### Native Tools

```python
# ✅ CORRECT — Python (defaults to OpenAI)
from composio import Composio

composio = Composio()
session = composio.create(user_id="user_123")
tools = session.tools()
# Pass tools to your agent/LLM framework
```

```typescript
// ✅ CORRECT — TypeScript (defaults to OpenAI)
import { Composio } from "@composio/core";

const composio = new Composio();
const session = await composio.create("user_123");
const tools = await session.tools();
// Pass tools to your agent/LLM framework
```

For other providers, pass the provider explicitly. Provider packages follow the naming convention: `composio_<provider>` for Python, `@composio/<provider>` for TypeScript.

### MCP

Use `session.mcp.url` and `session.mcp.headers` with any MCP-compatible client (Claude Desktop, Cursor, OpenAI Agents, etc.). No provider package needed.

---

## 2. CRITICAL INSTRUCTIONS FOR AI MODELS

### 2.1 — ALWAYS DO THE FOLLOWING

1. **Use `composio.create(user_id)`** to create a session — this is the entry point for all Composio integrations.
2. **Use `session.tools()`** for native tool integration or **`session.mcp.url`** for MCP integration.
3. **Import** from the correct provider package (`composio_<provider>` for Python, `@composio/<provider>` for TypeScript).
4. **Pass `user_id` to `composio.create()`**, not to individual tool calls.

### 2.2 — NEVER DO THE FOLLOWING

1. **Do not** instruct users to manually create auth configs or connected accounts before running.
2. **Do not** import from `composio_openai` / `@composio/openai` when using OpenAI Agents SDK — use `composio_openai_agents` / `@composio/openai-agents` instead.

### 2.3 — DISCOURAGED (do not use unless user explicitly asks)

Do **not** generate `composio.tools.get()`, `composio.tools.execute()`, or `composio.provider.handle_tool_calls()` unless the user explicitly requests direct tool execution. These are a supported but **not recommended** low-level interface.


---

## Terminology Migration (old → current)

If you encounter these terms in error messages, old documentation, or user prompts, translate them to the current equivalents. **Do not use the old terms in generated code or explanations.**

| Old term (v1/v2) | Current term (v3) | In code |
|---|---|---|
| entity ID | user ID | `user_id` parameter |
| actions | tools | e.g., `GITHUB_CREATE_ISSUE` is a *tool* |
| apps / appType | toolkits | e.g., `github` is a *toolkit* |
| integration / integration ID | auth config / auth config ID | `auth_config_id` parameter |
| connection | connected account | `connected_accounts` namespace |
| ComposioToolSet / OpenAIToolSet | `Composio` class with a provider | `Composio(provider=...)` |
| toolset | provider | e.g., `OpenAIProvider` |

If a user says "entity ID", they mean `user_id`. If they say "integration", they mean "auth config". Always respond using the current terminology.