Span attribute reference

Every attribute the plugin may set, grouped by span type. See Attribute conventions for the narrative version of the dual-convention mapping.

Attributes marked optional are only set when the underlying data is available.

Resource (on every span)

Attribute	Source
service.name	OTEL_PROJECT_NAME / project_name (fallback: hermes-agent)
service.version	hermes-otel plugin version
otel.scope.name	hermes-otel
openinference.project.name	Same as service.name
telemetry.sdk.*	Set by OTel SDK
any resource_attributes.*	From config.yaml
any global_tags.*	From config.yaml (overridden by resource_attributes on key conflict)

session.* / cron

Set at start:

Attribute	Type	Meaning
hermes.session.kind	string	cli · telegram · discord · cron · ...
hermes.session.id	string	Hermes session ID
session.id	string	Standard OTel alias
user.id	string	Hermes user ID (optional)

Set at end (turn summary):

Attribute	Type	Meaning
hermes.turn.tool_count	int	Distinct tool names invoked
hermes.turn.tools	string	Sorted CSV of distinct tool names (≤500 chars)
hermes.turn.tool_targets	string	|-joined distinct file paths/URLs
hermes.turn.tool_commands	string	|-joined distinct shell commands
hermes.turn.tool_outcomes	string	Sorted CSV of distinct outcome statuses
hermes.turn.skill_count	int	Distinct skills inferred
hermes.turn.skills	string	Sorted CSV of distinct skill names
hermes.turn.api_call_count	int	pre_api_request hooks fired
hermes.turn.final_status	string	completed · interrupted · incomplete · timed_out

Empty/zero aggregators are omitted.

llm.*

Span kind: LLM (OpenInference).

Attribute	Convention	Type	Meaning
llm.model_name	OpenInference	string	Model name
llm.provider	OpenInference	string	Provider (anthropic, openai, ...)
gen_ai.request.model	gen_ai	string	Model name (Langfuse)
gen_ai.system	gen_ai	string	Provider (Langfuse)
input.value	OpenInference	string	User message OR full conversation JSON
input.mime_type	OpenInference	string	text/plain OR application/json
output.value	OpenInference	string	Final assistant response
output.mime_type	OpenInference	string	text/plain
gen_ai.content.prompt	gen_ai	string	User message
gen_ai.content.completion	gen_ai	string	Assistant response
hermes.conversation.message_count	hermes	int	When conversation capture is on (optional)

api.*

Span kind: LLM (OpenInference).

Attribute	Convention	Type	Meaning
gen_ai.request.model	gen_ai	string	Model name
llm.model_name	OpenInference	string	Model name
llm.provider	OpenInference	string	Provider
llm.token_count.prompt	OpenInference	int	Prompt tokens
llm.token_count.completion	OpenInference	int	Completion tokens
llm.token_count.total	OpenInference	int	Sum
llm.token_count.cache_read	OpenInference	int	Cache read (optional)
llm.token_count.cache_write	OpenInference	int	Cache write (optional)
gen_ai.usage.input_tokens	gen_ai	int	Prompt tokens
gen_ai.usage.output_tokens	gen_ai	int	Completion tokens
gen_ai.usage.cache_read_input_tokens	gen_ai	int	Cache read (optional)
gen_ai.usage.cache_creation_input_tokens	gen_ai	int	Cache write (optional)
llm.invocation_parameters	OpenInference	string (JSON)	Request params
gen_ai.response.finish_reason	gen_ai	string	stop, tool_use, length, etc.
http.duration_ms	hermes	int	Wall-clock HTTP duration

tool.*

Span kind: TOOL (OpenInference).

Attribute	Convention	Type	Meaning
tool.name	OpenInference	string	Tool name
input.value	OpenInference	string	Tool args (JSON)
output.value	OpenInference	string	Tool result
hermes.tool.target	hermes	string	Inferred file path / URL (optional)
hermes.tool.command	hermes	string	Inferred shell command (optional)
hermes.tool.outcome	hermes	string	completed · error · timeout · blocked
hermes.skill.name	hermes	string	Inferred skill name (optional)

Metrics (separate from spans)

Emitted via PeriodicExportingMetricReader on backends that support OTLP metrics:

Metric	Type	Unit	Labels
hermes.tokens.prompt	Counter	tokens	model, provider
hermes.tokens.completion	Counter	tokens	model, provider
hermes.tokens.total	Counter	tokens	model, provider
hermes.tokens.cache_read	Counter	tokens	model, provider
hermes.tokens.cache_write	Counter	tokens	model, provider
hermes.tool.calls	Counter	count	tool_name, outcome
hermes.tool.duration	Histogram	ms	tool_name, outcome
hermes.api.duration	Histogram	ms	model, provider, finish_reason
hermes.skill.inferred	Counter	count	skill_name, source
hermes.sessions	Counter	count	kind, final_status

Label cardinality is bounded by normalised values (outcomes, finish reasons) and small dimension sets (model, tool name). No user IDs or other high-cardinality labels.