---
title: "logfmt | Grafana Loki documentation"
description: "The 'logfmt' Promtail pipeline stage. The logfmt parsing stage reads logfmt log lines and extracts the data into labels."
---

> For a curated documentation index, see [llms.txt](/llms.txt). For the complete documentation index, see [llms-full.txt](/llms-full.txt).

# logfmt

> Caution
> 
> Promtail has been deprecated and is in Long-Term Support (LTS) through February 28, 2026. Promtail will reach an End-of-Life (EOL) on March 2, 2026. You can find migration resources [here](/docs/alloy/latest/set-up/migrate/from-promtail/).

The `logfmt` stage is a parsing stage that reads the log line as [logfmt](https://brandur.org/logfmt) and allows extraction of data into labels.

## Schema

YAML ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```yaml
logfmt:
  # Set of key/value pairs for mapping of logfmt fields to extracted labels. The YAML key will be
  # the key in the extracted data, while the expression will be the YAML value. If the value
  # is empty, then the logfmt field with the same name is extracted.
  mapping:
    [ <string>: <string> ... ]

  # Name from extracted data to parse. If empty, uses the log message.
  [source: <string>]
```

This stage uses the [go-logfmt](https://github.com/go-logfmt/logfmt) unmarshaler, which means non-string types like numbers or booleans will be unmarshaled into those types. The extracted data can hold non-string values, and this stage does not do any type conversions; downstream stages will need to perform correct type conversion of these values as necessary. Please refer to the [`template` stage](../template/) for how to do this.

If the value extracted is a complex type, its value is extracted as a string.

## Examples

### Using log line

For the given pipeline:

YAML ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```yaml
- logfmt:
    mapping:
      timestamp: time
      app:
      duration:
      unknown:
```

Given the following log line:

![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```none
time=2012-11-01T22:08:41+00:00 app=loki level=WARN duration=125 message="this is a log line" extra="user=foo"
```

The following key-value pairs would be created in the set of extracted data:

- `timestamp`: `2012-11-01T22:08:41+00:00`
- `app`: `loki`
- `duration`: `125`

### Using extracted data

For the given pipeline:

YAML ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```yaml
- logfmt:
    mapping:
      extra:
- logfmt:
    mapping:
      user:
    source: extra
```

And the given log line:

![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```none
time=2012-11-01T22:08:41+00:00 app=loki level=WARN duration=125 message="this is a log line" extra="user=foo"
```

The first stage would create the following key-value pairs in the set of extracted data:

- `extra`: `user=foo`

The second stage will parse the value of `extra` from the extracted data as logfmt and append the following key-value pairs to the set of extracted data:

- `user`: `foo`