> For the complete documentation index, see [llms.txt](https://tarmac.gitbook.io/tarmac-framework/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://tarmac.gitbook.io/tarmac-framework/capabilities/functions.md).

# Functions

The Functions capability allows WASM functions to call other WASM functions. Unlike other callback capabilities, functions must register within the routes configuration within the `tarmac.json` configuration file.

## Function

```golang
_, err := wapc.HostCall("tarmac", "function", "function-name", []byte("Input to Function"))
```

### Interface Details

| Namespace | Capability | Function      | Input      | Output               |
| --------- | ---------- | ------------- | ---------- | -------------------- |
| `tarmac`  | `function` | Function Name | Input Data | Function Output Data |