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

# MCP Gateway Access Logs

> MCP-specific fields available in Tyk Gateway structured access logs, including JSON-RPC method, primitive type, primitive name, and error code.

When Tyk Gateway processes an MCP request, it adds four MCP-specific fields to the structured access log record for that request. These fields let you filter, aggregate, and analyze MCP traffic in your log management tooling using the same access log pipeline you use for REST APIs.

For an overview of all MCP observability signals, see [MCP observability](/nightly/ai-management/mcp-gateway/mcp-observability).

## Prerequisites

Access logging must be enabled in your Tyk Gateway configuration. Set `access_logs.enabled` to `true` in `tyk.conf`:

```json theme={null}
{
  "access_logs": {
    "enabled": true
  }
}
```

## MCP fields

The following fields are added to access log records for MCP requests. Each field is only included when it has a non-empty value; fields are omitted from the record entirely when not applicable, keeping log volume low on lifecycle calls such as `initialize` and `ping`.

| Field                | Type    | Description                                                                                                                           |
| -------------------- | ------- | ------------------------------------------------------------------------------------------------------------------------------------- |
| `api_type`           | string  | API protocol type. Always `mcp` for MCP requests.                                                                                     |
| `mcp_method`         | string  | JSON-RPC method invoked, for example `tools/call` or `resources/read`. Present on all MCP requests.                                   |
| `mcp_primitive_type` | string  | MCP primitive category: `tool`, `resource`, or `prompt`. Present only when a primitive was matched.                                   |
| `mcp_primitive_name` | string  | Name of the specific tool, resource, or prompt invoked, for example `get_current_weather`. Present only when a primitive was matched. |
| `mcp_error_code`     | integer | Gateway-mapped JSON-RPC error code. Present only when the request failed at the gateway layer.                                        |

The `mcp_error_code` field reflects errors that occur within the gateway: authentication failures, rate limit rejections, and upstream errors. It does not capture error codes from within the upstream MCP server's JSON-RPC response body.

| Error code | Meaning                      |
| ---------- | ---------------------------- |
| `-32001`   | Authentication required      |
| `-32002`   | Access denied                |
| `-32003`   | Rate limit exceeded          |
| `-32004`   | Upstream error (502/503/504) |
| `-32600`   | Invalid request (400)        |
| `-32603`   | Internal error (500)         |

## Configuring which fields to include

By default, when access logging is enabled, all available fields are included in each log record. To restrict the fields logged, set a `template` array in `access_logs`:

```json theme={null}
{
  "access_logs": {
    "enabled": true,
    "template": [
      "client_ip",
      "api_id",
      "api_name",
      "api_type",
      "method",
      "path",
      "status",
      "latency_total",
      "mcp_method",
      "mcp_primitive_type",
      "mcp_primitive_name",
      "mcp_error_code"
    ]
  }
}
```

When a `template` is configured, only the listed fields appear in each log record. Fields in the template that have no value for a given request are omitted.

## Example log records

A successful `tools/call` request produces a record similar to the following:

```json theme={null}
{
  "api_id": "my-weather-mcp",
  "api_name": "Weather MCP Proxy",
  "api_type": "mcp",
  "client_ip": "10.0.0.42",
  "latency_total": 312,
  "method": "POST",
  "mcp_method": "tools/call",
  "mcp_primitive_name": "get_current_weather",
  "mcp_primitive_type": "tool",
  "path": "/mcp",
  "prefix": "access-log",
  "status": 200
}
```

A request that fails at the gateway due to a missing or invalid key produces a record with `mcp_error_code` set and no primitive fields (the primitive was never reached):

```json theme={null}
{
  "api_id": "my-weather-mcp",
  "api_type": "mcp",
  "client_ip": "10.0.0.42",
  "latency_total": 4,
  "method": "POST",
  "mcp_error_code": -32001,
  "mcp_method": "tools/call",
  "path": "/mcp",
  "prefix": "access-log",
  "status": 401
}
```

An `initialize` lifecycle call produces a record with `mcp_method` set but no primitive fields:

```json theme={null}
{
  "api_id": "my-weather-mcp",
  "api_type": "mcp",
  "client_ip": "10.0.0.42",
  "latency_total": 18,
  "method": "POST",
  "mcp_method": "initialize",
  "path": "/mcp",
  "prefix": "access-log",
  "status": 200
}
```