Automatic attributes

Every span attribute the package writes — what it means, when it appears.

Every span produced by the auto-instrumentation includes a set of attributes out of the box. Some are unconditional, others appear under specific configurations.

Always present

Attribute	Type	Description
mcp.method.name	string	Always "tools/call" for tool invocations.
mcp.tool.name	string	The tool name passed to registerTool.
mcp.tool.title	string	Tool title from the tool config (may be undefined if not set).
mcp.tool.description	string	Tool description from the tool config.
mcp.request.id	string	UUID generated per request. Unique per call.
mcp.session.id	string	UUID generated when the SDK starts. Constant for the process.
mcp.operation.success	boolean	true on OK, false on thrown error.
mcp.operation.duration	number	Duration in ms.
client.address	string	First non-internal IPv4 address of the host. Falls back to "localhost".

Conditional

When enableArgumentCollection: true

Each tool argument is flattened into a mcp.request.argument.<key> attribute. Nested objects use dot notation.

mcp.request.argument.weightKg = 70
mcp.request.argument.heightM = 1.75
mcp.request.argument.metadata.locale = 'en-US'

Off by default — these often contain user input or PII.

When the handler is wrapped with safetyCheck

Attribute	Type	Description
mcp.safety_check.content	string	Original content passed to the safety API.
mcp.safety_check.flagged	boolean	true if Sedata’s API flagged the input.
mcp.safety_check.latency_ms	number	Round-trip latency of the safety check.
mcp.safety_check.success	boolean	true if the safety API responded OK (regardless of verdict).

When process.env.PORT is set

Attribute	Type	Description
client.port	string	Value of process.env.PORT.

On error

Attribute	Type	Description
error.type	string	Error class name (e.g. "TypeError").
error.message	string	Error message.

Resource attributes

Attached once per process and merged into every export:

Attribute	Source
service.name	config.serverName
service.version	config.serverVersion
mcp.session.id	UUID per process
Host / OS / env detector attrs	@opentelemetry/resources detectors

Filtering reference for dashboards

Common filter patterns:

service.name = "weather-mcp"
mcp.tool.name = "calculate-bmi"
mcp.operation.success = false
mcp.safety_check.flagged = true

See also

Tracing concept

How attributes get attached to spans.

Data processors

Mutate or remove attributes before export.