diff --git a/testing-tracing-opentelemetry/src/lib.rs b/testing-tracing-opentelemetry/src/lib.rs
index 00fdce8..8afc79a 100644
--- a/testing-tracing-opentelemetry/src/lib.rs
+++ b/testing-tracing-opentelemetry/src/lib.rs
@@ -16,7 +16,7 @@ pub fn assert_trace(
     is_trace_id_constant: bool,
 ) {
     let trace_id_0 = tracing_events
-        .get(0)
+        .first()
         .and_then(|v| v.as_object())
         .and_then(|v| v.get("span"))
         .and_then(|v| v.as_object())
diff --git a/tracing-opentelemetry-instrumentation-sdk/README.md b/tracing-opentelemetry-instrumentation-sdk/README.md
index 517ce85..1906a97 100644
--- a/tracing-opentelemetry-instrumentation-sdk/README.md
+++ b/tracing-opentelemetry-instrumentation-sdk/README.md
@@ -19,7 +19,7 @@ Instrumentation on the callee side of a call is  composed of steps:
 - do the processing
 - update attributes of the span with response (status,...)
 
-The crates provide helper (or inspiration) to extract/inject context info, start & update span and retrieve context or trace_id during processing (eg to inject trace_id into log, error message,...).
+The crates provide helper (or inspiration) to extract/inject context info, start & update span and retrieve context or `trace_id` during processing (eg to inject `trace_id` into log, error message,...).
 
 ```rust
   let trace_id = tracing_opentelemetry_instrumentation_sdk::find_current_trace_id();
@@ -31,8 +31,8 @@ The helpers could be used as is or into middleware build on it (eg: [`axum-traci
 ## Notes
 
 - [`tracing-opentelemetry`] extends [`tracing`] to interoperate with [OpenTelemetry]. But with some constraints:
-  - Creation of the OpenTelemetry's span is done when the tracing span is closed. So do not try to interact with OpenTelemetry Span (or SpanBuilder) from inside the tracing span.
-  - The OpenTelemetry parent Context (and trace_id) is created on `NEW` span or inherited from parent span. The parent context can be overwritten after creation, but until then the `trace_id` is the one from `NEW`, So tracing's log could report none or not-yet set trace_id on event `NEW` and the following until update.
+  - Creation of the OpenTelemetry's span is done when the tracing span is closed. So do not try to interact with OpenTelemetry Span (or `SpanBuilder`) from inside the tracing span.
+  - The OpenTelemetry parent `Context` (and `trace_id`) is created on `NEW` span or inherited from parent span. The parent context can be overwritten after creation, but until then the `trace_id` is the one from `NEW`, So tracing's log could report none or not-yet set `trace_id` on event `NEW` and the following until update.
   - To define kind, name,... of OpenTelemetry's span from tracing's span used special record's name: `otel.name`, `otel.kind`, ...
   - Record in a [`tracing`]'s Span should be defined at creation time. So some field are created with value `tracing::field::Empty` to then being updated.
 - Create trace with target `otel::tracing` (and level `trace`), to have a common way to enable / to disable
diff --git a/tracing-opentelemetry-instrumentation-sdk/src/span_type.rs b/tracing-opentelemetry-instrumentation-sdk/src/span_type.rs
index 37a0d9f..27d1702 100644
--- a/tracing-opentelemetry-instrumentation-sdk/src/span_type.rs
+++ b/tracing-opentelemetry-instrumentation-sdk/src/span_type.rs
@@ -1,3 +1,5 @@
+use std::fmt::Display;
+
 // SpanType is a non official open-telemetry key, only supported by Datadog, to help categorize traces.
 // Documentation: https://github.com/open-telemetry/opentelemetry-rust/blob/ccb510fbd6fdef9694e3b751fd01dbe33c7345c0/opentelemetry-datadog/src/lib.rs#L29-L30
 // Usage: It should be informed as span.type span key
@@ -19,9 +21,9 @@ pub enum SpanType {
     Graphql,
 }
 
-impl ToString for SpanType {
-    fn to_string(&self) -> String {
-        match self {
+impl Display for SpanType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let s = match self {
             SpanType::Web => "web",
             SpanType::Http => "http",
             SpanType::Sql => "sql",
@@ -35,7 +37,7 @@ impl ToString for SpanType {
             SpanType::Queue => "queue",
             SpanType::Consul => "consul",
             SpanType::Graphql => "graphql",
-        }
-        .to_owned()
+        };
+        f.write_str(s)
     }
 }