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The stdout exporter writes telemetry data to standard output, making it ideal for development, debugging, and learning. It supports all three OpenTelemetry signals: traces, metrics, and logs.
The stdout exporter is designed for development and debugging only. It is not optimized for production use, and the output format may change between versions.

​
Installation

Add the dependency to your Cargo.toml: 
[dependencies]
opentelemetry = "0.31"
opentelemetry_sdk = "0.31"
opentelemetry-stdout = "0.31"

​
Feature Flags

The stdout exporter supports selective signal features: 
# Default (all signals)
opentelemetry-stdout = "0.31"

# Traces only
opentelemetry-stdout = { version = "0.31", features = ["trace"], default-features = false }

# Metrics only
opentelemetry-stdout = { version = "0.31", features = ["metrics"], default-features = false }

# Logs only
opentelemetry-stdout = { version = "0.31", features = ["logs"], default-features = false }

​
Quick Start

​
Traces

use opentelemetry::global;
use opentelemetry::trace::Tracer;
use opentelemetry_sdk::trace::SdkTracerProvider;
use opentelemetry_sdk::Resource;
use opentelemetry_stdout::SpanExporter;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Create stdout exporter for traces
    let exporter = SpanExporter::default();

    // Create tracer provider
    let provider = SdkTracerProvider::builder()
        .with_simple_exporter(exporter)
        .with_resource(
            Resource::builder()
                .with_service_name("stdout-example")
                .build()
        )
        .build();

    global::set_tracer_provider(provider.clone());

    // Create and use a tracer
    let tracer = global::tracer("my-tracer");
    
    tracer.in_span("example-operation", |_cx| {
        println!("Doing some work...");
    });

    // Shutdown to flush spans
    provider.shutdown()?;
    Ok(())
}

​
Metrics

use opentelemetry::global;
use opentelemetry::KeyValue;
use opentelemetry_sdk::metrics::SdkMeterProvider;
use opentelemetry_sdk::Resource;
use opentelemetry_stdout::MetricExporter;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Create stdout exporter for metrics
    let exporter = MetricExporter::default();

    // Create meter provider
    let provider = SdkMeterProvider::builder()
        .with_periodic_exporter(exporter)
        .with_resource(
            Resource::builder()
                .with_service_name("stdout-example")
                .build()
        )
        .build();

    global::set_meter_provider(provider.clone());

    // Create and use a meter
    let meter = global::meter("my-meter");
    let counter = meter.u64_counter("requests").build();
    
    counter.add(1, &[KeyValue::new("endpoint", "/api/users")]);

    // Shutdown to flush metrics
    provider.shutdown()?;
    Ok(())
}

​
Logs

use opentelemetry_appender_tracing::layer::OpenTelemetryTracingBridge;
use opentelemetry_sdk::logs::SdkLoggerProvider;
use opentelemetry_sdk::Resource;
use opentelemetry_stdout::LogExporter;
use tracing::info;
use tracing_subscriber::prelude::*;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Create stdout exporter for logs
    let exporter = LogExporter::default();

    // Create logger provider
    let provider = SdkLoggerProvider::builder()
        .with_simple_exporter(exporter)
        .with_resource(
            Resource::builder()
                .with_service_name("stdout-example")
                .build()
        )
        .build();

    // Bridge tracing to OpenTelemetry
    let layer = OpenTelemetryTracingBridge::new(&provider);
    tracing_subscriber::registry().with(layer).init();

    // Use tracing macros
    info!("Application started");
    info!(user_id = "12345", "User logged in");

    // Shutdown to flush logs
    provider.shutdown()?;
    Ok(())
}

​
Complete Example (All Signals)

Here’s a comprehensive example that demonstrates all three signals: 
use once_cell::sync::Lazy;
use opentelemetry::{global, trace::{TraceContextExt, Tracer}, InstrumentationScope, KeyValue};
use opentelemetry_appender_tracing::layer::OpenTelemetryTracingBridge;
use opentelemetry_sdk::{
    logs::SdkLoggerProvider,
    metrics::SdkMeterProvider,
    trace::SdkTracerProvider,
    Resource,
};
use tracing::info;
use tracing_subscriber::prelude::*;

static RESOURCE: Lazy<Resource> = Lazy::new(|| {
    Resource::builder()
        .with_service_name("demo-app")
        .with_service_version("1.0.0")
        .build()
});

fn init_traces() -> SdkTracerProvider {
    let exporter = opentelemetry_stdout::SpanExporter::default();
    let provider = SdkTracerProvider::builder()
        .with_simple_exporter(exporter)
        .with_resource(RESOURCE.clone())
        .build();
    global::set_tracer_provider(provider.clone());
    provider
}

fn init_metrics() -> SdkMeterProvider {
    let exporter = opentelemetry_stdout::MetricExporter::default();
    let provider = SdkMeterProvider::builder()
        .with_periodic_exporter(exporter)
        .with_resource(RESOURCE.clone())
        .build();
    global::set_meter_provider(provider.clone());
    provider
}

fn init_logs() -> SdkLoggerProvider {
    let exporter = opentelemetry_stdout::LogExporter::default();
    let provider = SdkLoggerProvider::builder()
        .with_simple_exporter(exporter)
        .with_resource(RESOURCE.clone())
        .build();
    let layer = OpenTelemetryTracingBridge::new(&provider);
    tracing_subscriber::registry().with(layer).init();
    provider
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Initialize all providers
    let tracer_provider = init_traces();
    let meter_provider = init_metrics();
    let logger_provider = init_logs();

    // Create instrumentation scope
    let scope = InstrumentationScope::builder("demo-app")
        .with_version("1.0")
        .with_attributes([KeyValue::new("environment", "development")])
        .build();

    let tracer = global::tracer_with_scope(scope.clone());
    let meter = global::meter_with_scope(scope);

    // Create metrics
    let request_counter = meter
        .u64_counter("http_requests_total")
        .with_description("Total HTTP requests")
        .build();

    let request_duration = meter
        .f64_histogram("http_request_duration_seconds")
        .with_description("HTTP request duration")
        .build();

    // Record some metrics
    request_counter.add(1, &[
        KeyValue::new("method", "GET"),
        KeyValue::new("endpoint", "/api/users"),
    ]);
    request_duration.record(0.123, &[
        KeyValue::new("method", "GET"),
        KeyValue::new("status", "200"),
    ]);

    // Create traces with logs
    tracer.in_span("handle_request", |cx| {
        let span = cx.span();
        span.set_attribute(KeyValue::new("user.id", "12345"));
        span.set_attribute(KeyValue::new("request.path", "/api/users"));
        
        info!("Processing user request");
        
        span.add_event(
            "Request validated",
            vec![KeyValue::new("validation.time_ms", 5)],
        );
        
        tracer.in_span("database_query", |cx| {
            let span = cx.span();
            span.set_attribute(KeyValue::new("db.system", "postgresql"));
            info!("Querying database");
        });
        
        info!("Request completed successfully");
    });

    // Shutdown all providers
    tracer_provider.shutdown()?;
    meter_provider.shutdown()?;
    logger_provider.shutdown()?;

    Ok(())
}

​
Output Format

The stdout exporter prints telemetry in a human-readable JSON-like format:

​
Trace Output Example

Span {
    name: "handle_request",
    trace_id: 5b8aa5a2d2c872e8137a28db9d321b50,
    span_id: 5fb397be34d26b51,
    parent_span_id: 0000000000000000,
    start_time: 2026-03-02T12:00:00.123456Z,
    end_time: 2026-03-02T12:00:00.234567Z,
    attributes: {
        "user.id": "12345",
        "request.path": "/api/users"
    },
    events: [
        Event {
            name: "Request validated",
            timestamp: 2026-03-02T12:00:00.150000Z,
            attributes: {"validation.time_ms": 5}
        }
    ],
    status: Ok
}

​
Metric Output Example

Metric {
    name: "http_requests_total",
    description: "Total HTTP requests",
    unit: "",
    data: Sum {
        value: 1,
        attributes: {
            "method": "GET",
            "endpoint": "/api/users"
        }
    }
}

​
Log Output Example

LogRecord {
    timestamp: 2026-03-02T12:00:00.123456Z,
    severity: Info,
    body: "Processing user request",
    attributes: {},
    trace_id: 5b8aa5a2d2c872e8137a28db9d321b50,
    span_id: 5fb397be34d26b51
}

​
Configuration

​
Custom Writer

By default, output goes to stdout. You can customize the destination: 
use std::io::Write;
use opentelemetry_stdout::SpanExporter;

// Example: Write to a file
let file = std::fs::File::create("traces.log")?;
let exporter = SpanExporter::new(file);

​
Resource Configuration

Add resource attributes that appear in all telemetry: 
use opentelemetry::KeyValue;
use opentelemetry_sdk::Resource;

let resource = Resource::builder()
    .with_service_name("my-service")
    .with_service_version("1.2.3")
    .with_attributes([
        KeyValue::new("environment", "development"),
        KeyValue::new("region", "local"),
        KeyValue::new("host.name", "laptop"),
    ])
    .build();

let provider = SdkTracerProvider::builder()
    .with_simple_exporter(exporter)
    .with_resource(resource)
    .build();

​
Use Cases

​
Local Development

Quickly verify instrumentation without setting up a backend: 
let exporter = opentelemetry_stdout::SpanExporter::default();
let provider = SdkTracerProvider::builder()
    .with_simple_exporter(exporter)
    .build();

​
Testing

Validate telemetry data in tests: 
#[cfg(test)]
mod tests {
    use super::*;
    
    #[test]
    fn test_instrumentation() {
        let exporter = opentelemetry_stdout::SpanExporter::default();
        let provider = SdkTracerProvider::builder()
            .with_simple_exporter(exporter)
            .build();
        
        // Your test code that generates spans
        // Spans will be printed to stdout for inspection
    }
}

​
Learning and Education

Understand the structure of OpenTelemetry data: 
// Students can see exactly what data is being collected
let exporter = opentelemetry_stdout::SpanExporter::default();

​
Debugging Production Issues Locally

Reproduce issues with realistic data: 
// Switch to stdout exporter temporarily for debugging
#[cfg(debug_assertions)]
let exporter = opentelemetry_stdout::SpanExporter::default();

#[cfg(not(debug_assertions))]
let exporter = opentelemetry_otlp::SpanExporter::builder()
    .with_http()
    .build()?;

​
Performance Considerations

The stdout exporter writes synchronously and can block your application. It is not suitable for production use.

​
Impact on Application Performance

  • Each telemetry item is written immediately
  • I/O operations block the calling thread
  • Large volumes of telemetry can slow down your application
  • No batching or buffering

​
Alternatives for Production

For production, use:

​
Integration with Other Tools

​
Piping to jq

Format output with jq for better readability: 
cargo run | jq '.'

​
Filtering Output

Filter specific telemetry: 
# Only show errors
cargo run 2>&1 | grep -i error

# Only show spans
cargo run 2>&1 | grep "Span {"

​
Saving to File

Capture output for later analysis: 
cargo run > telemetry.log 2>&1

​
Troubleshooting

​
No Output Appearing

  1. Ensure shutdown is called: 
    provider.shutdown()?;  // Flushes all pending data
  2. Check feature flags: 
    opentelemetry-stdout = { version = "0.31", features = ["trace"] }
  3. Verify exporter is set: 
    let provider = SdkTracerProvider::builder()
    .with_simple_exporter(exporter)  // Must set exporter
    .build();

​
Output Mixed with Application Logs

Redirect stderr separately: 
cargo run 2>telemetry.log 1>app.log
Or use a custom writer: 
let file = std::fs::File::create("telemetry.log")?;
let exporter = opentelemetry_stdout::SpanExporter::new(file);

​
Performance Degradation

The stdout exporter is not optimized for high-volume telemetry. For production: 
// Switch to OTLP for production
let exporter = opentelemetry_otlp::SpanExporter::builder()
    .with_http()
    .build()?;

​
Comparison with Other Exporters

FeatureStdoutOTLPZipkin
Traces✓✓✓
Metrics✓✓✗
Logs✓✓✗
Production Ready✗✓✓
Batching✗✓✓
Backend Required✗✓✓
Use CaseDevelopmentProductionZipkin backends

​
Next Steps

OTLP Exporter

Production-ready exporter for all signals

Tracing Guide

Learn how to instrument your application

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