LayeredCraft.Logging.CompactJsonFormatter

A high-performance Serilog formatter that outputs compact JSON optimized for AWS CloudWatch metric filters and structured log analysis.

Overview

The standard Serilog CompactJsonFormatter uses @ prefixed properties for metadata (like @l for level, @t for timestamp, etc.). However, these @ prefixed properties are not compatible with AWS CloudWatch metric filters, which cannot parse escaped metadata keys.

This formatter solves that problem by replacing the @ prefix with _ (underscore) while maintaining all the performance benefits of the original compact formatter.

Key Features

• CloudWatch Compatible: Uses _ prefix instead of @ for metadata fields
• High Performance: Based on the official Serilog compact formatter
• Single-line JSON: Optimized for log ingestion and analysis
• Full Serilog Integration: Drop-in replacement for CompactJsonFormatter
• Trace Support: Includes trace ID and span ID support
• Multi-targeting: Supports .NET 8.0 and .NET 9.0

Installation

dotnet add package LayeredCraft.Logging.CompactJsonFormatter

Usage

Basic Usage

using LayeredCraft.Logging.CompactJsonFormatter;
using Serilog;

Log.Logger = new LoggerConfiguration()
    .WriteTo.Console(new CompactJsonFormatter())
    .CreateLogger();

Log.Information("Hello, {Name}!", "World");

With Custom Value Formatter

using LayeredCraft.Logging.CompactJsonFormatter;
using Serilog;
using Serilog.Formatting.Json;

var customValueFormatter = new JsonValueFormatter(typeTagName: "$type");

Log.Logger = new LoggerConfiguration()
    .WriteTo.Console(new CompactJsonFormatter(customValueFormatter))
    .CreateLogger();

AWS CloudWatch Integration

using LayeredCraft.Logging.CompactJsonFormatter;
using Serilog;
using Serilog.Sinks.AwsCloudWatch;

Log.Logger = new LoggerConfiguration()
    .WriteTo.AmazonCloudWatch(
        logGroup: "/aws/lambda/my-function",
        region: RegionEndpoint.USEast1,
        formatter: new CompactJsonFormatter())
    .CreateLogger();

Output Format

Standard Serilog CompactJsonFormatter Output

{"@t":"2025-01-14T10:30:00.000Z","@l":"Information","@mt":"Hello, {Name}!","Name":"World"}

LayeredCraft CompactJsonFormatter Output

{"_t":"2025-01-14T10:30:00.000Z","_l":"Information","_mt":"Hello, {Name}!","Name":"World"}

Field Mapping

Serilog Standard	LayeredCraft	Description
@t	_t	Timestamp
@l	_l	Log Level
@mt	_mt	Message Template
@m	_m	Rendered Message
@r	_r	Renderings
@x	_x	Exception
@tr	_tr	Trace ID
@sp	_sp	Span ID

CloudWatch Metric Filters

With the underscore prefix, you can easily create CloudWatch metric filters:

[_l="Error"]
[_l="Warning" && _t > "2025-01-01"]

Project Structure

compact-json-formatter/
├── src/
│   ├── LayeredCraft.Logging.CompactJsonFormatter.csproj
│   └── CompactJsonFormatter.cs
├── test/
│   └── LayeredCraft.Logging.CompactJsonFormatter.Tests.csproj
├── .github/
│   ├── workflows/
│   │   ├── build.yaml
│   │   └── pr-build.yaml
│   └── dependabot.yml
├── Directory.Build.props
├── README.md
├── CLAUDE.md
└── icon.png

Development

Building

dotnet build

Running Tests

dotnet test

Creating NuGet Package

dotnet pack

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests for your changes
5. Ensure all tests pass
6. Submit a pull request

License

This project is licensed under the MIT License - see the LICENSE file for details.

Related Projects

• LayeredCraft.StructuredLogging - Structured logging extensions for .NET