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

# Deploy an MCP server

> Stand up one Engine-hosted MCP server that reaches every service an agent is allowed to use.

An MCP server is an Engine-hosted runtime with its own URL. It never builds or downloads a package — apply stands it up, and it stays live until you deactivate it.

One server can span several internal and external services, so an agent needs one connection rather than one per provider.

## Author and deploy

```bash theme={null}
fused-cli mcp init support-agent \
  --service 'linear=v1' \
  --operation 'linear=issueUpdate' \
  --select-all 'slack'
```

That writes `.fused/mcps/support-agent.yaml`:

```yaml theme={null}
apiVersion: fused/v1
kind: mcp
name: support-agent
version: "1.0.0"
bucket: default
services:
  linear:
    version: "v1"
    operations: ["issueUpdate"]
    auth: { type: "oauth" }
    connect: { scopes: ["read:issues"] }
  slack:
    version: "v1"
    select_all: true
```

<Steps>
  <Step title="Validate">
    ```bash theme={null}
    fused-cli mcp validate
    ```
  </Step>

  <Step title="Preview">
    ```bash theme={null}
    fused-cli mcp plan
    ```
  </Step>

  <Step title="Stand it up">
    ```bash theme={null}
    fused-cli mcp apply
    fused-cli mcp list
    ```
  </Step>
</Steps>

<Warning>
  The first successful apply may return an execution token once. An idempotent apply will not reveal it again. Store it immediately.
</Warning>

## Flags

### `mcp init`

| Flag           | What it does                                                 | Example                                                       |
| -------------- | ------------------------------------------------------------ | ------------------------------------------------------------- |
| `--service`    | Adds a service at a version; repeatable                      | `fused-cli mcp init support --service 'linear=v1'`            |
| `--operation`  | Selects one operation; repeatable                            | `fused-cli mcp init support --operation 'linear=issueUpdate'` |
| `--select-all` | Takes every operation of a service                           | `fused-cli mcp init support --select-all 'slack'`             |
| `--extend`     | Adds to an existing config rather than refusing to overwrite | `fused-cli mcp init support --extend --select-all 'slack'`    |
| `--bucket`     | References an existing bucket; never creates one             | `fused-cli mcp init support --bucket agent-credentials`       |
| `--version`    | Sets the config version; defaults to `1.0.0`                 | `fused-cli mcp init support --version 2.0.0`                  |

`--language` is SDK-only. An MCP server is a runtime, not a generated package.

`mcp init` also resolves server-template variables for the operations you selected and writes the matching `server_variable` injections, reporting a count of what it generated. The behaviour is identical to the SDK side — [how init fills in routing](/app/build-an-sdk#init-fills-in-the-routing-you-would-otherwise-miss).

### `mcp plan`

| Flag            | What it does                                    | Example                                               |
| --------------- | ----------------------------------------------- | ----------------------------------------------------- |
| `--json`        | Prints the plan result and required permissions | `fused-cli mcp plan --json`                           |
| `--owner-team`  | Sets the owning team; defaults to you           | `fused-cli mcp plan --owner-team support`             |
| `--receipt-out` | Writes the receipt to a chosen path             | `fused-cli mcp plan --receipt-out ./ci/mcp.plan.json` |

MCP planning has no interactive credential remediation. That flag exists on SDK plans only.

### `mcp apply`

| Flag        | What it does                    | Example                                            |
| ----------- | ------------------------------- | -------------------------------------------------- |
| `--plan-id` | Applies one exact remote plan   | `fused-cli mcp apply --plan-id pln_6b2…`           |
| `--receipt` | Applies from a specific receipt | `fused-cli mcp apply --receipt ./ci/mcp.plan.json` |

`--download` and `--json` are SDK-only. An MCP server has no package to download.

## MCP-specific constraints

* **No webhooks.** `webhooks` and `webhooks_select_all` are rejected on an MCP config by both the CLI and the Engine. Treat event delivery as an SDK-only surface.
* **Unified operations require explicit targets.** A top-level `unified_operations` map uses the same bindings, dependencies, rollback, mapping, and output contract as an SDK. Each operation authorized by the execution token appears in `search_docs` and runs through the existing `execute` tool with `await call(operationId, {input, targets, selectors?, pagination?, idempotencyKey?})`. `targets` is always required, must be dependency-closed, and never defaults to every declared binding. See [declare a unified operation](/app/unified/declare) and [call a unified operation](/app/unified/call).
* **No implicit latest.** Every version reference is explicit.

## Versions

One MCP name has one stable MCP ID shared by every version, and each explicit version has its own immutable Version ID. Multiple versions can run at once.

Applying identical content to the same version is a no-op. Changing its operation, auth, or injection scope returns `app_version_immutable` — publish a new version instead.

## Deactivating

```bash theme={null}
fused-cli mcp deactivate support-agent@1.0.0
```

<Warning>
  This is irreversible. The Engine writes a tombstone, stops that runtime, and will not allow that MCP name and version to be recreated. Sibling versions and shared tokens survive.
</Warning>

Unlike removing a workspace service, deactivation is immediate and is not gated behind a blocker for configs that still reference it. There is no MCP deprecate or undeprecate command — do not invent one.

<Card title="Create a token for an agent" icon="shield-halved" href="/mcp/agent-tokens">
  A deployed server is not the same as a safe one. Narrow the token next.
</Card>