Composio vs custom MCP — which should I use?

Use Composio for pre-built actions across common SaaS apps (Slack, Gmail, Salesforce, Notion and 250+ more) — one API key, no integration work. Use a custom MCP server to expose your own internal tools, proprietary data, or an app Composio doesn't cover. Most teams use both.

Do I need to code anything to connect Composio?

No — paste your Composio API key into the Integrations page, then connect the specific apps you want with the per-app Connect buttons. No server to build or host.

How do I connect a custom MCP server to an AI agent?

Your server needs to speak MCP over Streamable-HTTP with the standard initialize handshake. Add its name, URL and auth details on the Integrations page, save, and the client discovers its tools automatically — they then load like any built-in tool.

Why can't the agent use an app I connected in the Composio dashboard?

A Composio API key alone only loads the catalog. The agent can only execute an app's actions after you connect that specific app from the Integrations card in this workspace — a connection made only in Composio's own dashboard isn't usable here.

Are writes through Composio or a custom MCP server approval-gated?

Yes — any write, whether it's an ad-account mutation, a Composio action (send a message, create a record) or a custom MCP tool call, pauses at the same approval gate before it runs. Connecting more tools doesn't change the write-safety model.

Concepts

Composio vs custom MCP: how to connect your AI agent to other tools

TL;DR

Composio and a custom MCP server both get your AI agent talking to tools beyond your ad platforms, and both work through the same Model Context Protocol — the difference is who built the integration. Composio is the fast path: one API key unlocks pre-built actions across 250+ SaaS apps (Slack, Gmail, HubSpot, Notion) you don't have to build yourself. A custom MCP server is the path for your own internal tools, proprietary data, or an app Composio doesn't cover — you host the endpoint, the agent discovers its tools automatically. Most teams end up using both.

The one-sentence difference

Composio is pre-built actions for common SaaS apps; a custom MCP server is the same protocol pointed at something you built yourself.

Side by side

	Composio	Custom MCP server
What it connects	250+ pre-built SaaS apps — Slack, Gmail, Sheets, HubSpot, Salesforce, Notion, Linear, GitHub…	Your own tools, internal systems or proprietary data, on an endpoint you host
Setup effort	One API key, then connect each app you want via its own OAuth	Build and host a Streamable-HTTP MCP endpoint; register its URL
Who maintains it	Composio maintains each app's action set	You maintain your own server
Best for	Fast access to common SaaS actions with zero integration work	Internal data, custom logic, or an app Composio doesn't support
Discovery	Automatic once the app is connected under your workspace	Automatic via the standard MCP tools/list handshake

How to connect Composio

1Sign in at app.composio.dev and go to Settings → API Keys to get a key (starts with "ak_").
2Paste the key into the Composio card on the Integrations page — it's verified live, then encrypted.
3Connect the specific apps you want using the per-app Connect buttons on the card. A key alone only loads the catalog; the agent can only execute an app's actions once you connect it from this workspace.
4Mention the app or the cross-app task in your goal — connected actions surface to the planner automatically when relevant.

Full walkthrough with troubleshooting: Connect & use Composio.

How to connect a custom MCP server

1Your server needs to speak MCP over Streamable-HTTP (JSON-RPC 2.0 over HTTP POST) with the standard initialize handshake.
2On the Integrations page, add its name, URL and — if needed — an auth header and token.
3Save & discover tools — the client runs the handshake and lists what your server exposes.
4Once discovered, your tools load automatically when a goal needs them, exactly like a built-in tool.

Full walkthrough: Add your own MCP server.

How to decide

Want to send a Slack message, create a Notion page, or append a Google Sheet — Composio. It's already built. (HubSpot is a native connection now, beside the ad platforms.)
Want the agent to reach an internal API, a proprietary database, or custom business logic — a custom MCP server, since nothing pre-built can expose data only you have.
Composio doesn't support the app you need — a custom MCP server pointed at that app's own API is the fallback.
You want both — completely normal. Composio for the common SaaS layer, a custom server for what's genuinely yours.

What stays the same either way

Reads from either source flow into the plan like any built-in tool. Writes — sending a message, creating a record, updating a system — pause at the same approval gate as an ad-account write, in-app or by email. Connecting more tools never means connecting more unsupervised writes.

Frequently asked questions

Composio vs custom MCP — which should I use?: Use Composio for pre-built actions across common SaaS apps (Slack, Gmail, Salesforce, Notion and 250+ more) — one API key, no integration work. Use a custom MCP server to expose your own internal tools, proprietary data, or an app Composio doesn't cover. Most teams use both.
Do I need to code anything to connect Composio?: No — paste your Composio API key into the Integrations page, then connect the specific apps you want with the per-app Connect buttons. No server to build or host.
How do I connect a custom MCP server to an AI agent?: Your server needs to speak MCP over Streamable-HTTP with the standard initialize handshake. Add its name, URL and auth details on the Integrations page, save, and the client discovers its tools automatically — they then load like any built-in tool.
Why can't the agent use an app I connected in the Composio dashboard?: A Composio API key alone only loads the catalog. The agent can only execute an app's actions after you connect that specific app from the Integrations card in this workspace — a connection made only in Composio's own dashboard isn't usable here.
Are writes through Composio or a custom MCP server approval-gated?: Yes — any write, whether it's an ad-account mutation, a Composio action (send a message, create a record) or a custom MCP tool call, pauses at the same approval gate before it runs. Connecting more tools doesn't change the write-safety model.