# Logging

Use the `PrismaClient` [`log`](/guides/reference-6-v6-reference-prisma-client-reference#log) parameter to configure [log levels](/guides/reference-6-v6-reference-prisma-client-reference#log-levels) , including warnings, errors, and information about the queries sent to the database.

Prisma Client supports two types of logging:

- Logging to [stdout](https://en.wikipedia.org/wiki/Standard_streams) (default)
- Event-based logging (use [`$on()`](/guides/reference-6-v6-reference-prisma-client-reference#on) method to [subscribe to events](#event-based-logging))

:::callout{intent="note"}
You can also use the `DEBUG` environment variable to enable debugging output in Prisma Client. See [Debugging](/guides/prisma-client-v6-debugging-and-troubleshooting-debugging) for more information.
:::

:::callout{intent="note"}
If you want a detailed insight into your Prisma Client's performance at the level of individual operations, see [Tracing](/guides/prisma-client-v6-observability-and-logging-opentelemetry-tracing).
:::

## [Log to stdout](#log-to-stdout)

The simplest way to print _all_ log levels to stdout is to pass in an array `LogLevel` objects:

```
const prisma = new PrismaClient({
  log: ["query", "info", "warn", "error"],
});
```

This is the short form of passing in an array of `LogDefinition` objects where the value of `emit` is always `stdout`:

```
const prisma = new PrismaClient({
  log: [
    {
      emit: "stdout",
      level: "query",
    },
    {
      emit: "stdout",
      level: "error",
    },
    {
      emit: "stdout",
      level: "info",
    },
    {
      emit: "stdout",
      level: "warn",
    },
  ],
});
```

## [Event-based logging](#event-based-logging)

To use event-based logging:

1. Set `emit` to `event` for a specific log level, such as query
2. Use the `$on()` method to subscribe to the event

The following example subscribes to all `query` events and write the `duration` and `query` to console:

:::code-group
```title="Relational databases"
const prisma = new PrismaClient({
  log: [
    {
      emit: "event",
      level: "query",
    },
    {
      emit: "stdout",
      level: "error",
    },
    {
      emit: "stdout",
      level: "info",
    },
    {
      emit: "stdout",
      level: "warn",
    },
  ],
});

prisma.$on("query", (e) => {
  console.log("Query: " + e.query);
  console.log("Params: " + e.params);
  console.log("Duration: " + e.duration + "ms");
});
```
:::

```
Query: SELECT "public"."User"."id", "public"."User"."email", "public"."User"."name" FROM "public"."User" WHERE 1=1 OFFSET $1
Params: [0]
Duration: 3ms
Query: SELECT "public"."Post"."id", "public"."Post"."title", "public"."Post"."authorId" FROM "public"."Post" WHERE "public"."Post"."authorId" IN ($1,$2,$3,$4) OFFSET $5
Params: [2, 7, 18, 29]
Duration: 2ms
```

:::code-group
```title="MongoDB"
const prisma = new PrismaClient({
  log: [
    {
      emit: "event",
      level: "query",
    },
    {
      emit: "stdout",
      level: "error",
    },
    {
      emit: "stdout",
      level: "info",
    },
    {
      emit: "stdout",
      level: "warn",
    },
  ],
});

prisma.$on("query", (e) => {
  console.log("Query: " + e.query);
});
```
:::

```
Query: db.User.aggregate([ { $project: { _id: 1, email: 1, name: 1, }, }, ])
Query: db.Post.aggregate([ { $match: { userId: { $in: [ "622f0bbbdf635a42016ee325", ], }, }, }, { $project: { _id: 1, slug: 1, title: 1, body: 1, userId: 1, }, }, ])
```

The exact [event (`e`) type and the properties available](/guides/reference-6-v6-reference-prisma-client-reference#event-types) depends on the log level.

## Related pages

- [Authentication & Tools](./authentication-tools-index.md)
- [Build](./build-index.md)
- [Changelog](../changelog.md)
- [Concepts](./concepts-index.md)
- [Console commands](./console-commands-index.md)
- [Contract Authoring](./contract-authoring-index.md)
- [Core Concepts](./core-concepts-index.md)
- [Data Modeling](./data-modeling-index.md)
- [Database](./database-index.md)
- [DB commands](./db-commands-index.md)

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