ZeroAlloc.Telemetry

Source-generated OpenTelemetry instrumentation for .NET.

Add [Instrument] to any interface and the generator emits a sealed proxy class that records Activity spans and Meter instruments per method — without reflection, params object[] boxing, or runtime attribute inspection.

Page	Description
Getting Started	Install and instrument your first interface
Attribute Reference	`[Instrument]`, `[Trace]`, `[Count]`, `[Histogram]`, `[CountFromResult]`, `[HistogramFromResult]`, `[MetricTagFromResult]`, `[MetricTag]`, `[MetricTagConstant]`, `[TraceTag]`, `[TraceTagFromResult]`, `[TraceTagConstant]`
Source Generator	What the generator emits — input/output examples
Testing	Assert spans and metrics with BCL listeners, no exporter needed
AOT & Trimming	Native AOT compatibility

Quick Example

[Instrument("MyApp.Orders")]
public interface IOrderService
{
    [Trace("order.create")]
    [Count("orders.created")]
    ValueTask<OrderId> CreateOrderAsync(CreateOrderCommand cmd, CancellationToken ct);

    [Trace("order.get")]
    [Histogram("order.get_ms")]
    ValueTask<Order> GetOrderAsync(OrderId id, CancellationToken ct);
}

The generator emits OrderServiceInstrumented : IOrderService. Wrap your implementation at the DI layer:

services.AddSingleton<OrderServiceImpl>();
services.AddSingleton<IOrderService>(sp =>
    new OrderServiceInstrumented(sp.GetRequiredService<OrderServiceImpl>()));

That's all. No OpenTelemetry SDK is required — ActivitySource and Meter are BCL types (net8.0+). Add exporters in your application startup independently.

Instruments at a Glance

Attribute	What it records	When
`[Trace("name")]`	`Activity` span	Every call — Error status and `error.type` on exception
`[Count("metric")]`	`Counter<long>` +1	Success only; with `When`, only when the guard is true
`[Histogram("metric")]`	`Histogram<double>` elapsed ms	Every call including on exception, tagged `error.type` there, unless `When` is set
`[CountFromResult("metric", "Member")]`	`Counter<long>` adds the member's value	Success only, when the member is not null
`[HistogramFromResult("metric", "Member")]`	`Histogram<double>` records the member's value	Success only, when the member is not null
`[MetricTagFromResult("tag", "Member")]`	A tag on the method's metrics	With each measurement, when a listener has enabled the instrument
`[MetricTag("tag")]` on a parameter	The argument, or a member of it, as a tag on the method's metrics	With each measurement, when a listener has enabled the instrument
`[MetricTagConstant("tag", value)]`	A constant tag on the method's metrics	With each measurement, when a listener has enabled the instrument
`[TraceTag("tag")]` on a parameter	`Activity.SetTag` with the argument, or a member of it	Right after the span starts
`[TraceTagFromResult("tag")]`	`Activity.SetTag` with the return value, or a member of it	After the call returns
`[TraceTagConstant("tag", value)]`	`Activity.SetTag` with a constant	Right after the span starts, before the argument tags

Contents​

Quick Example​

Instruments at a Glance​

Contents

Quick Example

Instruments at a Glance