Telemetry events emitted by LangEx.

LangEx uses :telemetry to emit structured events at key points during graph execution. All span events follow the [prefix, :start], [prefix, :stop], [prefix, :exception] convention produced by :telemetry.span/3.

Run-tree correlation

Every span's metadata carries two extra keys:

Graph invoke → step → node → LLM/checkpoint spans form a tree, so a single invocation can be fully reconstructed from the event stream. Subgraph invokes appear as child invoke spans of the parent node. See LangEx.Telemetry.Runs and, for exporting to OpenTelemetry, LangEx.Telemetry.OpenTelemetryBridge.

Events

[:lang_ex, :graph, :invoke, :start]

Emitted when a graph invocation begins.

• Measurements: %{system_time: integer(), monotonic_time: integer()}

• Metadata:

  Key	Type	Description
  :graph_id	atom() | nil	Graph identifier (first node key)
  :thread_id	term() | nil	Thread ID from config

[:lang_ex, :graph, :invoke, :stop]

Emitted when a graph invocation completes.

• Measurements: %{duration: integer(), monotonic_time: integer()}

• Metadata: same as start, plus:

  Key	Type	Description
  :result	atom	:ok, :interrupt, or :error

[:lang_ex, :graph, :invoke, :exception]

Emitted when a graph invocation raises.

• Measurements: %{duration: integer(), monotonic_time: integer()}
• Metadata: same as start, plus :kind, :reason, :stacktrace

[:lang_ex, :graph, :step, :start | :stop | :exception]

Emitted around each super-step.

• Metadata:

  Key	Type	Description
  :step	integer	Super-step number
  :active_nodes	[atom()]	Nodes executing in this step

[:lang_ex, :node, :execute, :start | :stop | :exception]

Emitted around individual node execution.

• Metadata:

  Key	Type	Description
  :node	atom()	Node name

[:lang_ex, :llm, :chat, :start | :stop | :exception]

Emitted around LLM provider chat calls (inside ChatModel nodes).

• Metadata:

  Key	Type	Description
  :provider	module()	LLM provider module
  :model	term()	Model name
  :message_count	integer	Number of messages sent

• Stop metadata adds:

  Key	Type	Description
  :status	atom	:ok or :error

[:lang_ex, :checkpoint, :save, :start | :stop | :exception]

Emitted around checkpoint persistence.

• Metadata:

  Key	Type	Description
  :checkpointer	module()	Checkpointer implementation
  :thread_id	term()	Thread identifier

[:lang_ex, :checkpoint, :load, :start | :stop | :exception]

Emitted around checkpoint loading.

• Metadata: same as :checkpoint, :save.