Last updated on Aug 27, 2026

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• SDK
• LangChain
• Observability
• Reference

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Event Model

OpenBox receives both governed middleware events and operational telemetry from the LangChain SDK. Understanding that model is necessary for writing policy, configuring guardrails, and interpreting the dashboard correctly.

Governance payloads on activity-boundary events also include a fallback_used field indicating whether a fail-safe path was used.

Top-Level Event Types

Event type	Emitted by	Primary use
WorkflowStarted	before_agent middleware hook	Start-of-run governance
WorkflowCompleted	after_agent middleware hook	Final outcome and summary telemetry
SignalReceived	User prompt extraction before the agent starts	Prompt-level context and auditability
LLMStarted	wrap_model_call before model execution	Input-time model governance and prompt guardrails
LLMCompleted	wrap_model_call after model execution	Output-time model governance, token usage, and response metadata
ToolStarted	wrap_tool_call before tool execution	Input-time tool governance and approvals
ToolCompleted	wrap_tool_call after tool execution	Output-time tool governance and tool result telemetry

Business Events Versus Internal Telemetry

In the LangChain SDK, business events are the middleware boundaries:

• agent run start and completion
• model call start and completion
• tool call start and completion

These are not separate business events:

• internal HTTP telemetry
• internal database telemetry
• internal file telemetry
• internal traced-function telemetry

Those appear as operational spans associated with the active model call, tool call, or agent run.

How Agent Runs Appear

LangChain agent runs are represented as workflow-like entities in OpenBox.

The middleware creates a run identity at before_agent time and uses the configured agent_name as the workflow type when present.

Important implications:

• A LangChain agent run can appear as a workflow run in OpenBox.
• The initiating prompt is emitted as SignalReceived(user_prompt).
• Model work is represented by LLMStarted and LLMCompleted, not as a tool activity.

Model Payload Shape Guidance

LLMStarted

Use LLMStarted to inspect prompt-side data.

Common fields:

• prompt
• activity_input[0].prompt
• activity_type = "llm_call"

LLMCompleted

Use LLMCompleted to inspect model response metadata.

Common fields:

• completion
• llm_model
• input_tokens
• output_tokens
• total_tokens
• has_tool_calls

Tool Payload Shape Guidance

ToolStarted

Use ToolStarted to inspect tool inputs and require approval before a tool executes.

Common fields:

• tool_name
• tool_type
• activity_type
• activity_input

ToolCompleted

Use ToolCompleted to inspect the tool output and final status.

Common fields:

• tool_name
• tool_type
• activity_output
• status
• duration_ms

Typical Event Sequences

Agent Run With A Model Call

SignalReceived(user_prompt)
-> WorkflowStarted
-> LLMStarted
-> zero or more telemetry spans during model execution
-> LLMCompleted
-> WorkflowCompleted

Tool Call

ToolStarted
-> zero or more telemetry spans during tool execution
-> ToolCompleted

Model Usage And Tool Health In The UI

• Model and token usage come from LLMCompleted metadata when the underlying model provider returns it.
• Tool health populates for agents that actually execute tools.
• An agent run that only generates text without tools may show model usage but no tool health.

Policy And Guardrail Guidance

Recommended approach:

1. Use LLMStarted for prompt-side model governance.
2. Use LLMCompleted for response-side model governance.
3. Use ToolStarted for tool-input guardrails and approval policies.
4. Use ToolCompleted for tool-output guardrails and result review.
5. Treat hook-triggered telemetry as internal by default.