prettylog

A human-readable, colorized slog.Handler for Go.
It formats log records as a single line with a timestamp, level, message, and indented JSON attributes, using 24-bit ANSI true-color via the standard image/color package.

Features

• Standard library only — uses image/color and color.Color; no external color dependencies.
• Customizable palette — override any or all colors with WithCustomColor.
• Semantic color names — colors are mapped to their usage (LevelDebug, Timestamp, Message, etc.) rather than raw color names.
• Zero-value fallback — when customizing, only the colors you specify are changed; the rest stay at their defaults.

Installation

go get github.com/yourname/prettylog

Quick start

package main

import (
 "log/slog"
 "os"

 "github.com/yourname/prettylog"
)

func main() {
 handler := prettylog.NewHandler(&slog.HandlerOptions{Level: slog.LevelDebug})
 logger := slog.New(handler)

 logger.Info("server started", "port", 8080)
 logger.Error("connection failed", "addr", "10.0.0.1", "retry", true)
}

Output (colors rendered in a compatible terminal):

[14:32:01.123] INFO: server started {
  "port": 8080
}
[14:32:01.124] ERROR: connection failed {
  "addr": "10.0.0.1",
  "retry": true
}

Default color scheme

Field	Default color	Description
LevelDebug	light grey	Levels ≤ slog.LevelDebug
LevelInfo	cyan	Levels ≤ slog.LevelInfo
LevelNotice	yellow	Custom levels between Info and Warn
LevelWarn	gold	slog.LevelWarn and levels between Warn and Error
LevelError	light red	slog.LevelError and levels up to Error+1
LevelFatal	light magenta	Levels > Error+1
Timestamp	blue	Record timestamp
Message	pink	Record message text
Attributes	dark grey	JSON-encoded attributes

Custom colors

Use WithCustomColor to override any part of the palette. Unchanged fields fall back to the defaults automatically.

package main

import (
 "image/color"
 "log/slog"

 "github.com/yourname/prettylog"
)

func main() {
 handler := prettylog.New(
  &slog.HandlerOptions{Level: slog.LevelDebug},
  prettylog.WithColor(),
  prettylog.WithCustomColor(prettylog.ColorMap{
   LevelError: color.RGBA{255, 0, 0, 255},   // bright red
   LevelFatal: color.RGBA{148, 0, 211, 255}, // violet
   Message:    color.RGBA{255, 255, 255, 255}, // white
  }),
 )

 logger := slog.New(handler)
 logger.Error("something went wrong")
}

Options

Option	Description
WithDestinationWriter(w io.Writer)	Set the output writer (default os.Stdout when using NewHandler).
WithColor()	Enable ANSI color output.
WithCustomColor(cm ColorMap)	Overlay a custom color map onto the defaults.
WithOutputEmptyAttrs()	Print {} when a record has no attributes instead of omitting them.

API

func New(handlerOptions *slog.HandlerOptions, options ...Option) *Handler

Creates a new Handler. If handlerOptions is nil, default options are used.

func NewHandler(opts *slog.HandlerOptions) *Handler

Convenience constructor equivalent to:

New(opts, WithDestinationWriter(os.Stdout), WithColor())

type ColorMap

type ColorMap struct {
 LevelDebug  color.Color // custom levels at or below slog.LevelDebug
 LevelInfo   color.Color // custom levels at or below slog.LevelInfo
 LevelNotice color.Color // custom levels between Info and Warn
 LevelWarn   color.Color // slog.LevelWarn and custom levels between Warn and Error
 LevelError  color.Color // slog.LevelError and custom levels up to Error+1
 LevelFatal  color.Color // custom levels above Error+1
 Timestamp   color.Color // record timestamp
 Message     color.Color // record message text
 Attributes  color.Color // JSON-encoded record attributes
}

Any field left as the zero value (RGBA{0,0,0,0}) falls back to the built-in default.

License

MIT