colorjson

A Go package that provides a colorized JSON handler for the Go standard library's slog package.

Features

• Pretty-prints JSON logs with syntax highlighting
• Color-coded log levels (INFO=green, DEBUG=cyan, WARN=yellow, ERROR=red)
• Properly formats and colorizes strings, numbers, booleans, and null values
• Implements the slog.Handler interface for seamless integration

Installation

go get github.com/hydronica/color-json

Usage

package main

import (
	"log/slog"
	"os"

	"github.com/hydronica/color-json"
)

func main() {
	// Create a new colorized JSON handler
	handler := colorjson.NewHandler(os.Stderr, &slog.HandlerOptions{
		Level: slog.LevelDebug, // Set minimum level
	})
	// customize colors
	handler.Colors.Brace = colorjson.GrayColor
	// background red, white text
	handler.Colors.LevelError = colorjson.BgRedColor + colorjson.WhiteColor

	// Create a logger with the handler
	logger := slog.New(handler)

	// Set as the default logger
	slog.SetDefault(logger)

	// Example log messages
	slog.Info("Server started", "addr", ":8080")
	slog.Debug("Detailed debug message", "value", 123)
	slog.Debug(`Testing null & escaped quotes: "`, "value", nil)
	slog.Warn("Something might be wrong", "error", "connection timeout")
	slog.Error("Critical error occurred", "error", "file not found", "details", map[string]interface{}{
		"path":        "/var/log/app.log",
		"code":        404,
		"permissions": false,
	})
}

Configuration

The NewHandler function accepts the same parameters as the standard slog.NewJSONHandler:

• w io.Writer - The output destination (typically os.Stderr)
• opts *slog.HandlerOptions - Handler options including:
  • Level - The minimum log level to output
  • AddSource - Whether to add source code information
  • ReplaceAttr - A function to customize log attribute handling

Output

The output will be colorized JSON with:

• JSON keys in cyan
• Strings in green
• Numbers in yellow
• Booleans in magenta
• Null values in bright white
• Braces/brackets in bright blue
• Log levels colored according to severity:
  • INFO: green
  • DEBUG: bright cyan
  • WARN: yellow
  • ERROR: red

Terminal Support

The colorization uses ANSI escape codes, which are supported by most modern terminals. If you're redirecting output to a file or using a terminal that doesn't support colors, you might see the raw ANSI codes.

License

GNU General Public License v3.0