# Manifest fields

The complete list of `SKILL.md` frontmatter fields HUSK reads. Any unrecognized key is preserved but ignored.

## Identity

| Field         | Type   | Required | Notes                                                 |
| ------------- | ------ | -------- | ----------------------------------------------------- |
| `name`        | string | yes      | Human-facing name; its kebab-case slug is the URL id. |
| `description` | string | yes      | One-line summary for cards and OpenAPI.               |

## Mode

| Field  | Type | Default | Notes                                                                          |
| ------ | ---- | ------- | ------------------------------------------------------------------------------ |
| `mode` | enum | derived | `script` (a `run` command), `static-file` (a `serve` file), `llm`, or `proxy`. |

`mode` is usually inferred: `proxy:` → `proxy`, `run` → `script`, `serve` → `static-file`, `tools` or neither `run` nor `serve` → `llm`. Set it explicitly for a pure-prompt `llm` skill.

## Script behavior

| Field   | Type           | Notes                                                                 |
| ------- | -------------- | --------------------------------------------------------------------- |
| `run`   | string or list | Kernel command. String is split on whitespace; list is used verbatim. |
| `serve` | string         | Path to a static file to return; no kernel runs.                      |

## LLM behavior (`mode: llm`)

| Field             | Type     | Default          | Notes                                                           |
| ----------------- | -------- | ---------------- | --------------------------------------------------------------- |
| `tools`           | list     | -                | Scripts the model may call (see below).                         |
| `tool_env`        | string\[] | `[]`             | Env var names a tool script may inherit; otherwise secret-free. |
| `provider`        | string   | `anthropic`      | `anthropic`, `openai`, `xai`, `google`, `deepseek`.             |
| `model`           | string   | provider default | The model id.                                                   |
| `max_tokens`      | number   | `4096`           | Output token cap (positive integer).                            |
| `max_tool_rounds` | number   | `10`             | Max LLM-to-tools rounds (positive integer).                     |

Each `tools` entry: `name`, `description`, `command` (argv string or list), and optional `parameters` (each `name`, `description`, `required`). Full semantics in [LLM skills & tools](/skills/llm). The system prompt is the `SKILL.md` body.

## Proxy behavior (`mode: proxy`)

| Field             | Type     | Default           | Notes                                                        |
| ----------------- | -------- | ----------------- | ------------------------------------------------------------ |
| `proxy`           | string   | -                 | Upstream URL (http/https). Setting it implies `mode: proxy`. |
| `headers`         | map      | -                 | Headers sent upstream; values may use `${VAR}` from env.     |
| `forward_headers` | string\[] | -                 | Incoming header names forwarded to the upstream.             |
| `proxy_method`    | string   | invocation method | Override the upstream HTTP method.                           |

Full semantics in [Proxy skills](/skills/proxy).

## I/O

| Field         | Type   | Default | Notes                                                   |
| ------------- | ------ | ------- | ------------------------------------------------------- |
| `input`       | enum   | `text`  | `text` (stdin), `file` (`$HUSK_INPUT_FILE`), or `none`. |
| `output`      | enum   | `text`  | `text` (stdout), `json` (stdout as JSON), or `file`.    |
| `input_mime`  | string | -       | Advertised MIME for `file` input (discovery hint).      |
| `output_mime` | string | -       | `Content-Type` used for `file` output responses.        |

## Execution

| Field        | Type   | Default | Notes                                                                   |
| ------------ | ------ | ------- | ----------------------------------------------------------------------- |
| `timeout_ms` | number | `60000` | Hard timeout. For script skills, the kernel; for `llm`, each tool call. |

## HTTP

| Field    | Type   | Default          | Notes                                        |
| -------- | ------ | ---------------- | -------------------------------------------- |
| `method` | enum   | `POST`           | `GET`, `POST`, `PUT`, `PATCH`, or `DELETE`.  |
| `route`  | string | `/skills/<slug>` | Custom invocation path; must start with `/`. |

## Unknown fields

Any frontmatter key not listed above (`price`, `token`, `capabilities`, ...) is preserved in the skill's `extra` but never acted on. See [Compatibility](/reference/compatibility).