Strands Agents
This page explains how to instrument a Strands Agents agent, how spans are identified, and how evaluation fields are extracted.
Topics
Instrument your agent
The Strands Agents SDK includes built-in telemetry and requires no additional instrumentation library. It produces spans and event records under the scope name strands.telemetry.tracer. When deployed on Amazon Bedrock AgentCore Runtime with the AWS Distro for OpenTelemetry (ADOT), the Runtime injects the session.id attribute and exports spans and event records automatically.
Instrumentation is one step in setting up observability. To export telemetry for evaluation, complete the full setup in Set up observability.
How spans are identified
Strands sets the gen_ai.operation.name attribute on each span. The evaluation service uses this attribute to classify spans:
| Span type |
Identifying attribute |
Example span name |
|
Invoke agent
|
gen_ai.operation.name = invoke_agent
|
invoke_agent TravelAgent
|
|
Execute tool
|
gen_ai.operation.name = execute_tool
|
execute_tool search_flights
|
|
Inference
|
gen_ai.operation.name = chat
|
chat
|
How evaluation fields are extracted
Where the conversation content sits depends on the telemetry delivery mode. With split telemetry, the content is in a separate event record. With unified telemetry, the content stays on the span, as events attached to it. For more information, see Telemetry setup and delivery. The identifying attribute (gen_ai.operation.name) is on the span in both modes.
From event records
With split telemetry, the service reads content from the event record correlated to each span:
-
User prompt: from the agent input messages (input.messages), the content of the message with a user role.
-
Agent response: from the agent output messages (output.messages), the content of the message with an assistant role.
-
Tool call: the tool name from the gen_ai.tool.name attribute on the execute tool span. The tool arguments and result come from that span’s event record (input and output).
For more information, see Example spans in split telemetry.
From inline span events
With unified telemetry, the same content is carried in inline span events instead of a separate event record:
-
User prompt: from the gen_ai.user.message event, the content attribute.
-
Agent response: from the gen_ai.choice event, the message attribute.
-
Tool call: the tool name from the gen_ai.tool.name attribute on the span. The tool arguments come from the gen_ai.tool.message event, and the result comes from the gen_ai.choice event.
For more information, see Example spans in unified telemetry.
Example spans in split telemetry
With split telemetry, the span carries the identifying attributes and the content lives in a correlated event record. The following examples are from a Strands travel-planning agent deployed on Amazon Bedrock AgentCore Runtime.
These examples are not complete spans. They show representative data from a real agent interaction, with some fields omitted and long values truncated for readability.
Example
- Invoke agent span
-
The gen_ai.operation.name attribute (invoke_agent) identifies this as an invoke agent span. The gen_ai.agent.tools attribute lists the tools available to the agent.
{
"traceId": "69e9cc4771d7cabe0d8e8cea33b6b338",
"spanId": "d24936b8989b6d42",
"parentSpanId": "0ff3498548044e4b",
"name": "invoke_agent TravelAgent",
"kind": "INTERNAL",
"scope": {
"name": "strands.telemetry.tracer",
"version": ""
},
"startTimeUnixNano": 1776929864011990383,
"endTimeUnixNano": 1776929869634304466,
"durationNano": 5622314083,
"attributes": {
"gen_ai.operation.name": "invoke_agent",
"gen_ai.system": "strands-agents",
"gen_ai.agent.name": "TravelAgent",
"gen_ai.request.model": "us.anthropic.claude-sonnet-4-20250514-v1:0",
"gen_ai.usage.input_tokens": 983,
"gen_ai.usage.output_tokens": 232,
"gen_ai.usage.total_tokens": 1215,
"gen_ai.agent.tools": "[\"search_flights\", \"book_flight\", \"search_hotels\", \"book_hotel\", \"search_activities\", \"book_activity\"]",
"session.id": "sea-nyc-trip-2-turns-adot_v17-20260423003743"
},
"status": {
"code": "OK"
}
}
The correlated event record carries the conversation content. The user prompt is the user-role message in input.messages, and the agent response is the assistant-role message in output.messages.
{
"spanId": "d24936b8989b6d42",
"traceId": "69e9cc4771d7cabe0d8e8cea33b6b338",
"scope": {
"name": "strands.telemetry.tracer"
},
"body": {
"input": {
"messages": [
{
"role": "user",
"content": "Hey, how can you help me"
}
]
},
"output": {
"messages": [
{
"role": "assistant",
"content": {
"message": "Hi there! I'm your travel planning assistant ...",
"finish_reason": "end_turn"
}
}
]
}
}
}
- Execute tool span
-
The gen_ai.operation.name attribute (execute_tool) identifies this as an execute tool span. The gen_ai.tool.name attribute holds the tool name.
{
"traceId": "69e9cc4d132b180909ba49f613f273dd",
"spanId": "fff785ce12d6fda8",
"parentSpanId": "96915bf5ecc78743",
"name": "execute_tool search_flights",
"kind": "INTERNAL",
"scope": {
"name": "strands.telemetry.tracer",
"version": ""
},
"startTimeUnixNano": 1776929872258292842,
"endTimeUnixNano": 1776929872259611427,
"durationNano": 1318585,
"attributes": {
"gen_ai.operation.name": "execute_tool",
"gen_ai.tool.name": "search_flights",
"gen_ai.tool.call.id": "tooluse_hiWwdtThuD67G5cK8cp5mj",
"gen_ai.tool.status": "success",
"gen_ai.tool.description": "Search for available flights between cities.",
"session.id": "sea-nyc-trip-2-turns-adot_v17-20260423003743"
},
"status": {
"code": "OK"
}
}
The correlated event record carries the tool input (arguments) and output (result).
{
"spanId": "fff785ce12d6fda8",
"traceId": "69e9cc4d132b180909ba49f613f273dd",
"scope": {
"name": "strands.telemetry.tracer"
},
"body": {
"input": {
"messages": [
{
"role": "tool",
"content": {
"content": "{\"origin\": \"SEA\", \"destination\": \"NYC\", \"date\": \"2025-03-15\"}",
"role": "tool",
"id": "tooluse_hiWwdtThuD67G5cK8cp5mj"
}
}
]
},
"output": {
"messages": [
{
"role": "assistant",
"content": {
"message": "[{\"text\": \"{\\\"origin\\\": \\\"SEA\\\", \\\"destination\\\": \\\"NYC\\\", \\\"flights\\\": [ ... ]}\"}]",
"id": "tooluse_hiWwdtThuD67G5cK8cp5mj"
}
}
]
}
}
}
Example spans in unified telemetry
With unified telemetry, the same content is carried in inline span events on the span, with no separate event record. The following examples are from a Strands travel-planning agent.
These examples are not complete spans. They show representative data from a real agent interaction, with some fields omitted and long values truncated for readability.
Example
- Invoke agent span
-
The gen_ai.user.message event holds the user prompt, and the gen_ai.choice event holds the agent response.
{
"traceId": "69e9cc4771d7cabe0d8e8cea33b6b338",
"spanId": "d2ee0e4765cc773e",
"name": "invoke_agent TravelAgent",
"kind": "INTERNAL",
"scope": {
"name": "strands.telemetry.tracer"
},
"attributes": {
"gen_ai.operation.name": "invoke_agent",
"gen_ai.agent.name": "TravelAgent",
"session.id": "sea-nyc-trip-2-turns-unified"
},
"events": [
{
"name": "gen_ai.user.message",
"attributes": {
"content": "[{\"text\": \"Hey, how can you help me\"}]"
}
},
{
"name": "gen_ai.choice",
"attributes": {
"message": "Hi there! I'm your travel planning assistant ...",
"finish_reason": "end_turn"
}
}
]
}
- Execute tool span
-
The gen_ai.tool.message event holds the tool arguments, and the gen_ai.choice event holds the tool result.
{
"traceId": "69e9cc4d132b180909ba49f613f273dd",
"spanId": "0a988e27758ebb53",
"name": "execute_tool search_flights",
"kind": "INTERNAL",
"scope": {
"name": "strands.telemetry.tracer"
},
"attributes": {
"gen_ai.operation.name": "execute_tool",
"gen_ai.tool.name": "search_flights",
"gen_ai.tool.call.id": "tooluse_JuGterOaZfQV2c55Rp3S7C",
"gen_ai.tool.status": "success",
"session.id": "sea-nyc-trip-2-turns-unified"
},
"events": [
{
"name": "gen_ai.tool.message",
"attributes": {
"content": "{\"origin\": \"SEA\", \"destination\": \"NYC\", \"date\": \"2025-03-15\"}",
"role": "tool",
"id": "tooluse_JuGterOaZfQV2c55Rp3S7C"
}
},
{
"name": "gen_ai.choice",
"attributes": {
"message": "[{\"text\": \"{\\\"origin\\\": \\\"SEA\\\", \\\"destination\\\": \\\"NYC\\\", \\\"flights\\\": [ ... ]}\"}]",
"id": "tooluse_JuGterOaZfQV2c55Rp3S7C"
}
}
]
}
