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

# Overview

> Enable built-in and custom tools in Messages.

Tools let the assistant run targeted operations (like searching artifacts, analyzing tabular data, or extracting a web page) as part of a message response.

You enable tools by adding three fields to a `POST /messages` request:

| Field          | Purpose                                                                           |
| -------------- | --------------------------------------------------------------------------------- |
| `tools`        | Which tools are allowed.                                                          |
| `tool_choice`  | How the assistant should choose tools (`auto`, force a specific tool, or `none`). |
| `tool_context` | Optional context artifacts (documents or database connections).                   |

## Prerequisites

* An API token. See [Backoffice Developer Console](/en/developer-manual/get-started/developer-console).
* Your Zylon hostname (replace `{BASE_URL}` in the examples).

## Basic request and response

When you’re iterating on tool configuration, start with `POST /messages/validate` to validate your request body without running a model.

This example enables the **web fetch** tool:

```bash theme={null}
curl -X POST "https://{BASE_URL}/api/gpt/v1/messages/validate" \
  -H "Authorization: Bearer {API_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "default",
    "max_tokens": 64,
    "messages": [
      { "role": "user", "content": "Summarize: https://example.com/" }
    ],
    "tools": [
      { "name": "web_extract", "type": "web_extract_v1" }
    ],
    "tool_choice": { "type": "auto" }
  }'
```

<Accordion title="Example response">
  ```json theme={null}
  { "valid": true, "errors": null }
  ```
</Accordion>

To actually run the request, send the same body to `POST /messages`.

## Built-in tools

Zylon includes a set of built-in tools you can enable by name + type:

| Tool type             | What it does                                     | Requires `tool_context`   |
| --------------------- | ------------------------------------------------ | ------------------------- |
| `semantic_search_v1`  | Search ingested artifacts                        | Yes (`ingested_artifact`) |
| `tabular_analysis_v1` | Analyze tabular artifacts                        | Yes (`ingested_artifact`) |
| `web_extract_v1`      | Fetch and extract a URL mentioned in the message | No                        |
| `web_search_v1`       | Search the web from a natural language query     | No                        |
| `database_query_v1`   | Query a SQL database from natural language       | Yes (`sql_database`)      |

Guides:

* [Semantic Search tool](/en/developer-manual/build-with-zylon/tools/built-in/semantic-search-tool)
* [Tabular Analysis tool](/en/developer-manual/build-with-zylon/tools/built-in/tabular-analysis-tool)
* [Web Fetch tool](/en/developer-manual/build-with-zylon/tools/built-in/web-fetch-tool)
* [Web Search tool](/en/developer-manual/build-with-zylon/tools/built-in/web-search-tool)
* [Database Query tool](/en/developer-manual/build-with-zylon/tools/built-in/database-query-tool)

## Custom tools

Custom tools let you define your own tool interface using JSON Schema. When the assistant chooses your tool, it returns a `tool_use` content block with structured `input`.

See: [Custom tools](/en/developer-manual/build-with-zylon/tools/custom/custom-tools)

## Common mistakes

* **Using the wrong field name**: tool schemas use `inputSchema` (not `input_schema`).
* **Missing tool context**: `semantic_search_v1`, `tabular_analysis_v1`, and `database_query_v1` need `tool_context`.
* **Forgetting auth**: include `Authorization: Bearer ...` on every request.

## Next steps

* Learn the Messages request format: [Messages](/en/developer-manual/build-with-zylon/working-with-messages)
* Ingest content for retrieval and analysis: [Artifacts](/en/developer-manual/build-with-zylon/working-with-artifacts)