---
name: "jl"
section: "1"
platform: "linux"
package: "jl"
version: "0.1.0+git20220705+8771236337c6-1+b11"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/jl"
---

# jl(1)

pretty-print JSON logs

## NAME

jl - pretty-print JSON logs

## SYNOPSIS

**jl** \[*options...*\] \[*file*\]

## DESCRIPTION

**jl** is a parser and formatter for JSON logs, making machine-readable JSON logs human readable again.

**jl** consumes JSON logs from stdin and writes human-readable logs to stdout. To use **jl**, just pipe your JSON logs through it:

```
    ./my-app-executable | jl
    cat app-log.json | jl
```

**jl** can read from a file:

```
    jl my-app-log.json
```

**jl** itself doesn't support following log files, but since it can consume from a pipe, you can use **tail**:

```
    tail -F app-log.json | jl
```

You can page **jl**'s colorised output using **less** with the **-R** flag:

```
    jl my-app-log.json | less -R
```

## OPTIONS

A summary of options is included below.

- **-color** **auto**\|**yes**\|**no**

  Set the color mode. The options are "auto", "yes", and "no". "auto" disables color if stdout is not a TTY (default: "auto")

- **-format** **compact**\|**logfmt**

  Formatter for logs. The options are "compact" and "logfmt" (default: "compact")

- **-truncate**\[**=false**\]

  Whether to truncate strings in the compact formatter (default: true)

## FORMATTERS

**jl** currently supports two formatters, with plans to make the formatters customizable.

The default is **-format compact**, which extracts only important fields from the JSON log, like **message**, **timestamp**, **level**, colorises and presents them in a easy to skim way. It drops unrecognised fields from the logs.

The other option is **-format logfmt**, which formats the JSON logs in a way that closely resembles logfmt This option emits all fields from each log line.

Both formatters echo non-JSON log lines as-is.

## LOG FORMATS

JSON application logs tend to have some core shared fields, like **level**, **timestamp**, and **message** which **jl** tries to discover and prioritise for formatting. For now, the following formats work best with **jl**. For string fields other than **level**, only the keys matter.

Other formats can be used after preprocessing with **jq**.

- •

  Java-like:

  ```
      {
        "level": "error",
        "timestamp": "2019-02-02 15:39:45",
        "logger": "HelloWorldService",
        "thread": "main",
        "message": "hello world",
        "exception": "java.lang.IllegalArgumentException: The world isn't here\n...stacktraces..."
      }
  ```

- •

  Go/Logrus-like:

  ```
      {
        "level": "error",
        "timestamp": "2019-02-02 15:39:45",
        "msg": "hello world",
        "error": "hello error",
        "stack": "\nhello\n\thello.go\nworld\n\tworld.go"
      }
  ```

## COPYRIGHT

Copyright (C) 2019-2023 Yunchi Luo

License: MIT/Expat

This manual page is based on the README document by the author. It was reformatted and adapted by Andrej Shadura \<andrewsh@debian.org\> for the Debian project, and is distributed under the same license as the original project.

## SEE ALSO

[**jq**(1)](/jq/1.md), \<https://blog.codeship.com/logfmt-a-log-format-thats-easy-to-read-and-write/\>