Tagattribute

Stable Telemetry SourceGenerator Reviewed 2026-09-01 purview-dev/telemetry-sourcegenerator activity c-sharp distributed-tracing dotnet events high-performance-logging instrumentation logging melt metrics nuget observability open-telemetry open-telemetry-csharp otel roslyn source-generator spans telemetry tracing

TagAttribute

The TagAttribute is used within Activity and Metric generation to specify how parameters are added as tags.

In v4, tag names follow the configured NamingConvention:

OpenTelemetry (default): Uses snake_case for compound words (e.g., "entity_id")
Legacy: Uses lowercase smashed format (e.g., "entityid")

TagAttribute Properties

Name	Type	Default	Description
Name	`string?`	`null`	Explicitly sets the name of the tag. When `null`, the parameter name is used (and transformed according to NamingConvention).
SkipOnNullOrEmpty	`bool`	`false`	When `true`, the tag is not added if the parameter value is `null` or default.

Usage Examples

using Purview.Telemetry;

[ActivitySource("OrderService")]
interface IOrderTelemetry
{
    [Activity]
    Activity? ProcessingOrder(
        // Auto-named tag (becomes "order_id" in OpenTelemetry mode)
        [Tag]int orderId,

        // Explicitly named tag
        [Tag(Name = "customer.name")]string customerName,

        // Skip if null
        [Tag(SkipOnNullOrEmpty = true)]string? notes
    );
}

Tag Naming in v4

The tag name generation depends on the NamingConvention setting:

OpenTelemetry Convention (default):

[Tag]int orderId       // Generated: "order_id"
[Tag]string userName   // Generated: "user_name"
[Tag(Name = "my.custom.tag")]int value  // Generated: "my.custom.tag" (explicit names not transformed)

Legacy Convention:

[Tag]int orderId       // Generated: "orderid"
[Tag]string userName   // Generated: "username"

To change the convention, see Generation - Naming Conventions.

Best Practices

Use explicit names for cross-service tags - Prevents issues if parameter names change:
```
[Tag(Name = "trace.id")]string traceId
```
Use SkipOnNullOrEmpty for optional tags - Avoids cluttering telemetry with null values:
```
[Tag(SkipOnNullOrEmpty = true)]string? optionalContext
```
Follow OpenTelemetry semantic conventions - Use standard names like http.method, http.status_code, service.name:
```
[Tag(Name = "http.method")]string method
[Tag(Name = "http.status_code")]int statusCode
```

Compound words: Let v4’s OpenTelemetry mode handle it automatically:

// Good - auto-transforms to "customer_id"
[Tag]int customerId

// Also good - explicit naming
[Tag(Name = "customer.id")]int id