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

# Extensions

> Author and bind ECP (Execution Control Protocol) extensions: catalog on import, string bindings, and package boundaries.

# Extensions

Extensions add capabilities to an ECP (Execution Control Protocol) environment: model providers, formats, memory, secrets, and more.

## Catalog and bind

Extension packages should call `catalogExtension(def)` at module load so string ids resolve:

```ts theme={null}
import "@executioncontrolprotocol/format-toon"
import { extension } from "@executioncontrolprotocol/node"

extension("@executioncontrolprotocol/format-toon").with({})
```

Prefer **npm package name === extension id** (for example `@executioncontrolprotocol/format-toon`).

`ensureBoundExtensionsRegistered()` runs automatically before encode, decode, describe, and run when using the core environment path — you typically do not need a separate register step for cataloged packages.

## Definitions vs invocations

| Layer   | API                                                         |
| ------- | ----------------------------------------------------------- |
| Define  | `defineExtension(ns, name).withCapabilities([...]).build()` |
| Catalog | `catalogExtension(def)` on package load                     |
| Bind    | `extension("@scope/name").with({…})` in an environment      |
| Invoke  | `step("@scope/name.capability", "Label").with({…})`         |

## Package boundaries

Extensions depend on `@executioncontrolprotocol/types` and `@executioncontrolprotocol/core` (plus focused third-party libs). They must **not** import:

* `@executioncontrolprotocol/node`
* `@executioncontrolprotocol/browser`
* `@executioncontrolprotocol/cli`
* `@executioncontrolprotocol/mcp`

Hosts wrap core; extensions stay portable.

## First-party and vendor

Protocol/platform extensions live in the ECP monorepo (formats, providers such as Ollama and Chrome AI, memory, secrets, …). Vendor integrations (fal, Slack, image-sharp, Adobe, …) ship from the sibling [executioncontrolprotocol-extensions](https://github.com/GuillaumeCleme/executioncontrolprotocol-extensions) repository.

In-repo testing stub:

```ts theme={null}
import "@executioncontrolprotocol/core/testing"
extension("@executioncontrolprotocol/test").with({})
```

## Next steps

* [Environments](/guides/environments)
* [Fluent API](/guides/fluent-api)
* [Packages](/reference/packages)