> ## Documentation Index
> Fetch the complete documentation index at: https://ctrlrun.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Choosing between them

> In-process Python: the decorator. Tools behind MCP: the gateway. A framework with its own approval UI: an adapter.

In-process Python takes the decorator, tools behind MCP take the gateway, and a framework with
its own approval UI takes an adapter. The decision is about where the call that acts lives, not
about which framework you use.

## The decision table

| Where the call that acts lives                                          | Use                     | Because                                                                                    |
| ----------------------------------------------------------------------- | ----------------------- | ------------------------------------------------------------------------------------------ |
| A Python function you can decorate, in the agent's process              | `@protect`              | It sees the real arguments, raises refusals as exceptions, and needs nothing installed     |
| A tool server the agent reaches over MCP, in any language               | the gateway             | The agent and the server stay as they are; the gateway sits between them                   |
| A LangGraph graph whose humans answer with `Command(resume=...)`        | `ctrlrun-langgraph`     | The approval request goes through `interrupt()` rather than raising past the graph         |
| An OpenAI Agents SDK run whose humans answer with `state.approve(item)` | `ctrlrun-openai-agents` | The approval request goes through the SDK's tool-approval interruption                     |
| A framework with no human-in-the-loop primitive                         | `@protect`              | There is nothing for an adapter to reuse                                                   |
| Both a decorated function and an MCP server                             | both                    | They share one policy and one store; an effect key reserved by one is refused by the other |

Two questions settle most cases. Can you decorate the function that acts? Then the decorator.
Does your framework already have a place where a human says yes? Then, and only then, an
adapter routes the request there.

## What you don't need on one host

For a single host, the whole of the default configuration is a policy file and a directory:

| You do not need                        | Because                                                                                                                                            |
| -------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------- |
| a server                               | the decorator and the store run in your process                                                                                                    |
| a database                             | the store is a SQLite file, `.ctrlrun/state.db`, beside your policy; reservation is atomic across processes on that host through `BEGIN IMMEDIATE` |
| a dashboard                            | receipts are JSON lines beside the store, and `ctrlrun receipts`, `inspect` and `stats` read them                                                  |
| a message queue or an approval service | `ctrlrun approve` writes the grant; a webhook provider can route the request to Slack when you want that                                           |
| an identity provider                   | `ctrlrun.context(agent=...)` names the principal; a header or JWT provider replaces it when the process is fronted by something that authenticates |

When the store has to be shared across hosts, that is the one thing that changes:
[Run on Postgres](/guides/run-on-postgres).

## What changes nothing

The three ways in share one policy, one store, one set of guarantees and one receipt format. A
refund refused by the gateway is refused for the same reason and recorded in the same shape as
one refused by the decorator, and `ctrlrun verify` checks the configuration behind all three.

## Next

* [60-second quickstart](/get-started/quickstart), for the decorator.
* [Put the gateway in front of MCP](/guides/gateway-in-front-of-mcp).
* [Why](/why).


## Related topics

- [Three ways in](/get-started/three-ways-in.md)
- [CTRLRun](/index.md)
- [Put the gateway in front of MCP](/guides/gateway-in-front-of-mcp.md)
- [Install](/get-started/install.md)
- [Protect an existing MCP server in five minutes](/cookbook/protect-an-mcp-server.md)