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OpenTelemetry B3 propagator provides context propagation for systems that are using the B3 header format

Version published

Package description

What is @opentelemetry/propagator-b3?

The @opentelemetry/propagator-b3 npm package is used for B3 propagation format which is a convention for passing trace context information across service boundaries. It supports both single-header and multi-header encoding. This package is part of the OpenTelemetry project which provides a collection of tools, APIs, and SDKs to instrument, generate, collect, and export telemetry data (metrics, logs, and traces) to help analyze a software's performance and behavior.

What are @opentelemetry/propagator-b3's main functionalities?

B3 Propagation

This feature allows the user to extract and inject B3 propagation headers. The B3Propagator can be set as the global propagator in OpenTelemetry.

const { B3Propagator } = require('@opentelemetry/propagator-b3');
const { propagation } = require('@opentelemetry/api');

// Use the B3Propagator for extracting and injecting
propagation.setGlobalPropagator(new B3Propagator());

B3 Multi-header Propagation

This feature supports the B3 multi-header propagation format, which uses multiple headers to transmit tracing information. It is useful when interacting with systems that expect B3 headers in multiple header format.

const { B3MultiPropagator } = require('@opentelemetry/propagator-b3');
const { propagation } = require('@opentelemetry/api');

// Use the B3MultiPropagator for extracting and injecting with multi-header support
propagation.setGlobalPropagator(new B3MultiPropagator());

Other packages similar to @opentelemetry/propagator-b3




:books: (Refine Doc)

  • refactor(examples): added usage of @opentelemetry/semantic-conventions and @opentelemetry/resources to the examples in examples/opentelemetry-web for maintaining consistency across all examples. #4764 @Zen-cronic

:house: (Internal)

  • refactor(context-zone-peer-dep): use explicit exports #4785 @pichlermarc
  • refactor(context-async-hooks): use explicit exports #4785 @pichlermarc



OpenTelemetry Propagator B3

NPM Published Version Apache License

The OpenTelemetry b3 propagator package provides multiple propagator implementations for systems using the b3 context format. See the b3 specification for complete details.

B3 Formats

Single-Header Format:

b3: {TraceId}-{SpanId}-{SamplingState}-{ParentSpanId}

Multi-Header Format:

X-B3-TraceId: {TraceId}
X-B3-SpanId: {SpanId}
X-B3-ParentSpanId: {ParentSpanId}
X-B3-Sampled: {SamplingState}
  • {TraceId}

    • Required
    • Encoded as 32 or 16 lower-hex characters
    • 16 character traceIds will be converted to 32 characters by left-padding with 0s to conform with the OpenTelemetry specification
  • {SpanId}

    • Required
    • Encoded as 16 lower-hex characters
  • {ParentSpanId}

    • Optional
    • Used to support the Zipkin functionality where the client and server spans that make up an HTTP request share the same id
    • Not propagated by this library
  • {SamplingState} - Single-header

    • Optional
    • Valid values
      • 1 - Accept
      • 0 - Deny
      • d - Debug
      • Absent - Defer sampling decision
  • {SamplingState} - Multi-header

    • Optional
    • Valid values
      • 1 - Accept
      • 0 - Deny
  • {Flags} - Multi-header

    • Optional
    • Debug is encoded as X-B3-Flags: 1. Absent or any other value can be ignored. Debug implies an accept decision, so don't also send the X-B3-Sampled header.

B3 Propagation

The default B3Propagator implements b3 propagation according to the OpenTelemetry specification. It extracts b3 context from multi and single header encodings and injects context using the single-header b3 encoding by default. The inject encoding can be changed to multi-header via configuration. See the examples below.

B3 Single-Header Configuration

const api = require('@opentelemetry/api');
const { B3Propagator } = require('@opentelemetry/propagator-b3');

api.propagation.setGlobalPropagator(new B3Propagator());

B3 Multi-Header Configuration

const api = require('@opentelemetry/api');
const { B3Propagator, B3InjectEncoding } = require('@opentelemetry/propagator-b3');

  new B3Propagator({ injectEncoding: B3InjectEncoding.MULTI_HEADER })

B3 Single and Multi-Header Configuration

The B3Propagator always extracts both the single and multi-header b3 encodings. If you need to inject both encodings this can accomplished using a composite propagator.

const api = require('@opentelemetry/api');
const { CompositePropagator } = require('@opentelemetry/core');
const { B3Propagator, B3InjectEncoding } = require('@opentelemetry/propagator-b3');
  new CompositePropagator({
    propagators: [
      new B3Propagator(),
      new B3Propagator({ injectEncoding: B3InjectEncoding.MULTI_HEADER }),


Apache 2.0 - See LICENSE for more information.



Package last updated on 20 Jun 2024

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