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Compact JSON event format for Serilog
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Serilog.Formatting.Compact Build status NuGet

A simple, compact JSON-based event format for Serilog. CompactJsonFormatter significantly reduces the byte count of small log events when compared with Serilog's default JsonFormatter, while remaining human-readable. It achieves this through shorter built-in property names, a leaner format, and by excluding redundant information.


A simple Hello, {User} event.

{"@t":"2016-06-07T03:44:57.8532799Z","@mt":"Hello, {User}","User":"nblumhardt"}

Getting started

Install from NuGet:

Install-Package Serilog.Formatting.Compact

The formatter is used in conjunction with sinks that accept ITextFormatter. For example, the file sink:

Log.Logger = new LoggerConfiguration()
  .WriteTo.File(new CompactJsonFormatter(), "./logs/myapp.json")

To specify the formatter in XML <appSettings> provide its assembly-qualified type name:

  <add key="serilog:using:File" value="Serilog.Sinks.RollingFile" />
  <add key="serilog:write-to:File.path" value="./logs/myapp.json" />
  <add key="serilog:write-to:File.formatter"
       value="Serilog.Formatting.Compact.CompactJsonFormatter, Serilog.Formatting.Compact" />

Rendered events

CompactJsonFormatter will preserve the message template, properties, and formatting information so that the rendered message can be created at a later point. When the JSON is intended for consumption in an environment without message template rendering, RenderedCompactJsonFormatter can be used instead.

Instead of the message template, RenderedCompactJsonFormatter writes the fully-rendered message, as well as an event id generated from the message template, into the event:

{"@t":"2016-06-07T03:44:57.8532799Z","@m":"Hello, \"nblumhardt\"","@i":"7a8b9c0d","User":"nblumhardt"}

Format details

The format written by the compact formatters is specified generically so that implementations for other logging libraries, including Microsoft.Extensions.Logging, are possible if desired.


Each event is a JSON object with event data at the top level. Any JSON property on the payload object is assumed to be a regular property of the event, apart from the reified properties below.

Reified properties

The format defines a handful of reified properties that have special meaning:

Property Name Description Required?
@t Timestamp An ISO 8601 timestamp Yes
@m Message A fully-rendered message describing the event
@mt Message Template Alternative to Message; specifies a message template over the event's properties that provides for rendering into a textual description of the event
@l Level An implementation-specific level identifier (string or number) Absence implies "informational"
@x Exception A language-dependent error representation potentially including backtrace
@i Event id An implementation specific event id (string or number)
@r Renderings If @mt includes tokens with programming-language-specific formatting, an array of pre-rendered values for each such token May be omitted; if present, the count of renderings must match the count of formatted tokens exactly

The @ sigil may be escaped at the start of a user property name by doubling, e.g. @@name denotes a property called @name.

Batch format

When events are batched into a single payload, a newline-delimited stream of JSON documents is required. Either \n or \r\n delimiters may be used. Batches of newline-separated compact JSON events can use the (unofficial) MIME type application/vnd.serilog.clef.


Versioning would be additive only, with no version identifier; implementations should treat any unrecognised reified properties as if they are user data.


The output and benchmarks below compare the compact JSON formatter with Serilog's built-in JsonFormatter.


Log.Information("Hello, {@User}, {N:x8} at {Now}",
    Name = "nblumhardt",
    Tags = new[] { 1, 2, 3 }

Default JsonFormatter 292 bytes

emplate":"Hello, {@User}, {N:x8} at {Now}","Properties":{"User":{"Name":"nblumha

CompactJsonFormatter 187 bytes (0.64)

{"@t":"2016-06-07T03:44:57.8532799Z","@mt":"Hello, {@User}, {N:x8} at {Now}","@r

Formatting benchmark

See test/Serilog.Formatting.Compact.Tests/FormattingBenchmarks.cs.

Formatter Median StdDev Scaled
JsonFormatter 11.2775 µs 0.0682 µs 1.00
CompactJsonFormatter 6.0315 µs 0.0429 µs 0.53
RenderedJsonFormatter 13.7585 µs 0.1194 µs 1.22
RenderedCompactJsonFormatter 7.0680 µs 0.0605 µs 0.63


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