🛈 Note: This is pre-release documentation for the upcoming tracing 0.2.0 ecosystem.

For the release documentation, please see docs.rs, instead.

Crate tracing_serde

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An adapter for serializing tracing types using serde.

Documentation Documentation (master)


tracing is a framework for instrumenting Rust programs to collect scoped, structured, and async-aware diagnostics.tracing-serde enables serializing tracing types using serde.

Traditional logging is based on human-readable text messages. tracing gives us machine-readable structured diagnostic information. This lets us interact with diagnostic data programmatically. With tracing-serde, you can implement a Collector to serialize your tracing types and make use of the existing ecosystem of serde serializers to talk with distributed tracing systems.

Serializing diagnostic information allows us to do more with our logged values. For instance, when working with logging data in JSON gives us pretty-print when we’re debugging in development and you can emit JSON and tracing data to monitor your services in production.

The tracing crate provides the APIs necessary for instrumenting libraries and applications to emit trace data.

Compiler support: requires rustc 1.49+


First, add this to your Cargo.toml:

tracing = "0.1"
tracing-serde = "0.1"

Next, add this to your crate:

use tracing_serde::AsSerde;

Please read the tracing documentation for more information on how to create trace data.

This crate provides the as_serde function, via the AsSerde trait, which enables serializing the Attributes, Event, Id, Metadata, and Record tracing values.

For the full example, please see the examples folder.

Implement a Collector to format the serialization of tracing types how you’d like.

use tracing_serde::AsSerde;
use serde_json::json;

pub struct JsonSubscriber {
    next_id: AtomicUsize, // you need to assign span IDs, so you need a counter

impl Collect for JsonSubscriber {

    fn new_span(&self, attrs: &Attributes<'_>) -> Id {
        let id = self.next_id.fetch_add(1, Ordering::Relaxed);
        let id = Id::from_u64(id as u64);
        let json = json!({
        "new_span": {
            "attributes": attrs.as_serde(),
            "id": id.as_serde(),
        println!("{}", json);

    fn event(&self, event: &Event<'_>) {
        let json = json!({
           "event": event.as_serde(),
        println!("{}", json);

    // ...

After you implement your Collector, you can use your tracing subscriber (JsonSubscriber in the above example) to record serialized trace data.

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-serde = { version = "0.2", default-features = false }

    Note:tracing-serde’s no_std support requires liballoc.

Supported Rust Versions

Tracing is built against the latest stable release. The minimum supported version is 1.49. 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 1.45, the minimum supported version will not be increased past 1.42, 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.


Support for serializing fields as serde structs or maps.


Implements tracing_core::field::Visit for some serde::ser::SerializeMap.
Implements tracing_core::field::Visit for some serde::ser::SerializeStruct.
Implements serde::Serialize to write Attributes data to a serializer.
Implements serde::Serialize to write Event data to a serializer.
Implements serde::Serialize to write Record data to a serializer.