tracing-core 0.1.32

Core primitives for application-level tracing.

Tracing — Structured, application-level diagnostics


Core primitives for application-level tracing. Documentation Documentation (master) MIT licensed Build Status Discord chat

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tracing is a framework for instrumenting Rust programs to collect structured, event-based diagnostic information. This crate defines the core primitives of tracing.

The crate provides:

  • span::Id identifies a span within the execution of a program.

  • Event represents a single event within a trace.

  • Subscriber, the trait implemented to collect trace data.

  • Metadata and Callsite provide information describing spans and events.

  • Field, FieldSet, Value, and ValueSet represent the structured data attached to spans and events.

  • Dispatch allows spans and events to be dispatched to Subscribers.

In addition, it defines the global callsite registry and per-thread current dispatcher which other components of the tracing system rely on.

Compiler support: requires rustc 1.56+


Application authors will typically not use this crate directly. Instead, they will use the tracing crate, which provides a much more fully-featured API. However, this crate's API will change very infrequently, so it may be used when dependencies must be very stable.

Subscriber implementations may depend on tracing-core rather than tracing, as the additional APIs provided by tracing are primarily useful for instrumenting libraries and applications, and are generally not necessary for Subscriber implementations.

Crate Feature Flags

The following crate feature flags are available:

  • std: Depend on the Rust standard library (enabled by default).

    no_std users may disable this feature with default-features = false:

    tracing-core = { version = "0.1.31", default-features = false }

    Note:tracing-core's no_std support requires liballoc.

Supported Rust Versions

Tracing is built against the latest stable release. The minimum supported version is 1.56. The current Tracing version is not guaranteed to build on Rust versions earlier than the minimum supported version.

Tracing follows the same compiler support policies as the rest of the Tokio project. The current stable Rust compiler and the three most recent minor versions before it will always be supported. For example, if the current stable compiler version is 1.69, the minimum supported version will not be increased past 1.69, three minor versions prior. Increasing the minimum supported compiler version is not considered a semver breaking change as long as doing so complies with this policy.


This project is licensed under the MIT license.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tokio by you, shall be licensed as MIT, without any additional terms or conditions.