# API Caller Tool
## Description
The `api_caller` tool is a versatile Go-based gRPC service that performs an HTTP request to a specified URL. It is designed for interacting with external services via REST APIs and supports GET, POST, PUT, and DELETE methods.
## Parameters
The tool accepts the following arguments in a JSON object:
| Parameter | Type | Required | Default | Description |
|-------------|----------|----------|---------|-----------------------------------------------------------------------------|
| `url` | `string` | **Yes** | | The full URL of the API endpoint to call. |
| `method` | `string` | No | `GET` | The HTTP method to use (e.g., `GET`, `POST`, `PUT`, `DELETE`). |
| `headers` | `object` | No | | An optional JSON object of key-value pairs to be sent as request headers. |
| `json_body` | `object` | No | | An optional JSON object to be sent as the request body for `POST` or `PUT`. |
**Note:** When `json_body` is provided, the `Content-Type` header is automatically set to `application/json`.
## Response
The tool's response depends on the content of the API's reply:
* **JSON Response:** If the API returns a valid JSON body, the tool will parse it and return a JSON object.
* **Text Response:** If the API returns a non-JSON body (e.g., plain text, HTML), the tool will return it as a single string.
* **Error:** If the HTTP request fails (e.g., network error, non-2xx status code) or has a timeout (15 seconds), the tool returns an error message.
## Usage Example
Here is an example of how to use the `api_caller` tool to post data to a hypothetical `/users` API endpoint. This example uses `curl` to interact with the MCP server's HTTP/REST gateway.
**Request:**
```bash
curl -X POST http://localhost:8002/v1/tools:run \
-d '{
"name": "api_caller",
"arguments": {
"url": "https://api.example.com/v1/users",
"method": "POST",
"headers": {
"Authorization": "Bearer your_api_key_here"
},
"json_body": {
"name": "John Doe",
"email": "john.doe@example.com"
}
}
}'
```
**Successful Response (JSON):**
If the API call is successful, the tool might return a JSON object like this:
```json
{
"result": {
"structValue": {
"fields": {
"id": { "stringValue": "user_12345" },
"status": { "stringValue": "created" }
}
}
}
}
```
## Configuration
The tool's configuration is managed through a `config.json` file located in the tool's directory.
**Example `config.json`:**
```json
{
"port": 50051,
"command": ["go", "run", "."]
}
```
* `port`: The port on which the tool's gRPC server will listen.
* `command`: The command and arguments to execute the tool.
## Health and Logging
* **Health Checks:** This tool implements the standard gRPC Health Checking Protocol. The main MCP server will not route requests to it if it is unhealthy.
* **Logging:** The tool uses a structured JSON logger (`slog`) to log all operations to standard output for observability.
