LangSmith Engine webhook events

Reference for the webhook events the LangSmith Engine sends when it creates issues or links new traces to existing issues.

LangSmith Engine is in Beta and under active development. To provide feedback or use this feature, reach out to the LangChain team.

Forward LangSmith-detected agent issues into your incident-management, paging, or chat tools. LangSmith Engine sends a webhook event to your endpoint when it opens a new issue, or when it links a new trace to an issue it has already opened.

To configure webhook subscriptions, open the Issue Settings panel on the Issues tab of a tracing project. See Configure the LangSmith Engine.

Delivery

LangSmith sends a POST request with a JSON body to your webhook URL. The request uses Content-Type: application/json and includes any custom headers you attached to the subscription.

Property	Value
Method	POST
Body	JSON, common envelope below
Scheme	http:// and https:// are accepted. https:// is strongly recommended
Timeout	20 seconds per attempt
Attempts	Up to 4 attempts (1 initial plus 3 retries with exponential backoff) on transport errors or HTTP responses >= 400
Response	Success is determined from the status code alone. Response bodies are ignored.

Retries deliver a byte-identical payload, including the same id. Dedupe on id so a retried delivery does not produce a duplicate downstream effect.

Custom headers

You can attach arbitrary headers to each subscription (for example, Authorization: Bearer …) to authenticate the caller at your endpoint. Content-Type is always set by LangSmith and cannot be overridden.

Severity filtering

Each subscription has a severity_threshold from 0 to 3. An event is delivered only when the issue’s severity is less than or equal to the threshold. Lower numbers are more urgent.

Severity	Meaning
0	Urgent
1	High
2	Medium
3	Low

For example, a subscription with severity_threshold: 1 receives events for URGENT (0) and HIGH (1) issues only.

Event-type filtering

Each subscription specifies the event types it wants to receive. Subscriptions created without an explicit list default to ["issue.created"].

Event envelope

Every event delivered to your endpoint uses the same outer JSON shape.

Field	Type	Description
id	UUID	Unique identifier for this delivery. Stable across retries. Use it to dedupe.
type	string	Event type. One of issue.created or issue.trace.added.
created	integer	Unix seconds (UTC) when the event was enqueued.
request_id	UUID	Shared by every event fired from the same upstream action. See Batch coalescing.
data	object	Event payload. Always contains data.object. Contains data.trace only on issue.trace.added events.

data.object

data.object is a snapshot of the issue and is included on every event, regardless of type. Treat it as the authoritative state of the issue at the time the event was generated.

Field	Type	Description
id	UUID	Issue ID.
name	string	Short title of the issue.
description	string	Human-readable description.
severity	integer	0 (urgent) through 3 (low). See Severity filtering.
tenant_id	UUID	Workspace the issue belongs to.
tenant_name	string	Workspace display name (best-effort). Empty if the workspace has been deleted.
session_id	UUID	Tracing project the issue belongs to.
session_name	string	Tracing project name (best-effort). Empty if the project has been deleted.
url	string	Deep link to the issue in the LangSmith UI.

data.trace

data.trace is included only on issue.trace.added events.

Field	Type	Description
run_id	UUID	ID of the run that was linked to the issue.
trace_id	UUID	ID of the trace that contains the run.
start_time	string	RFC 3339 timestamp of when the run started.
comment	string | null	Optional note recorded when the trace was linked. Omitted when empty.

Batch coalescing

A single upstream action can produce multiple webhook events. When the Engine opens a new issue and attaches five traces to it, you receive one issue.created event and five issue.trace.added events, all sharing the same request_id. Use request_id to group these into a single downstream notification.

Event types

The event types below are the complete set the LangSmith Engine sends today. New types may be added in the future, so handlers should ignore unknown type values rather than failing.

issue.created

Sent when the LangSmith Engine creates a new issue. data.trace is omitted.

{
  "id": "b91c1f0e-7c4a-4f53-9d3e-9f1c8e7a2b10",
  "type": "issue.created",
  "created": 1747238400,
  "request_id": "0d2f4f6a-2a3a-4b6e-9b87-5d5b6e8c9a01",
  "data": {
    "object": {
      "id": "9a8b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d",
      "name": "Tool selection inconsistency",
      "description": "Agent repeatedly calls the search tool with identical arguments before terminating.",
      "severity": 1,
      "tenant_id": "11111111-2222-3333-4444-555555555555",
      "tenant_name": "Acme Workspace",
      "session_id": "66666666-7777-8888-9999-aaaaaaaaaaaa",
      "session_name": "prod-api",
      "url": "https://smith.langchain.com/o/11111111-2222-3333-4444-555555555555/projects/p/66666666-7777-8888-9999-aaaaaaaaaaaa?tab=5&issue=9a8b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d"
    }
  }
}

issue.trace.added

Sent when a new trace is linked to an existing issue. data.trace describes the linked trace.

{
  "id": "c02e3a4b-5c6d-7e8f-9a0b-1c2d3e4f5a6b",
  "type": "issue.trace.added",
  "created": 1747238410,
  "request_id": "0d2f4f6a-2a3a-4b6e-9b87-5d5b6e8c9a01",
  "data": {
    "object": {
      "id": "9a8b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d",
      "name": "Tool selection inconsistency",
      "description": "Agent repeatedly calls the search tool with identical arguments before terminating.",
      "severity": 1,
      "tenant_id": "11111111-2222-3333-4444-555555555555",
      "tenant_name": "Acme Workspace",
      "session_id": "66666666-7777-8888-9999-aaaaaaaaaaaa",
      "session_name": "prod-api",
      "url": "https://smith.langchain.com/o/11111111-2222-3333-4444-555555555555/projects/p/66666666-7777-8888-9999-aaaaaaaaaaaa?tab=5&issue=9a8b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d"
    },
    "trace": {
      "run_id": "f1e2d3c4-b5a6-9788-6655-44332211ffee",
      "trace_id": "abcdefab-1234-5678-9abc-def012345678",
      "start_time": "2026-05-14T12:30:00Z",
      "comment": "Reproduces the same tool-loop pattern."
    }
  }
}

Test your endpoint

Before pointing a real subscription at your endpoint, send a sample payload to verify it accepts and acknowledges within the 20-second timeout:

curl -X POST https://your-endpoint.example.com/webhook \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $WEBHOOK_SECRET" \
  -d @sample-issue-created.json

Use the example body from issue.created as sample-issue-created.json. Verify that:

• The custom Authorization header arrives and matches the secret you configured on the subscription.
• The handler persists the event keyed by its id so retries are deduped.
• The handler returns 2xx before kicking off slow downstream work.

Security

• Webhook URLs are validated when the subscription is created and again at delivery time. Private and metadata IP ranges are blocked in SaaS. Both http:// and https:// are accepted; use https:// so the payload and any custom headers are not sent in cleartext.
• LangSmith does not sign webhook bodies. Authenticate the sender by setting a secret as a custom header on the subscription (for example, Authorization: Bearer …) and verifying it at your endpoint. Anyone with the webhook URL can POST to it, so treat the URL itself as confidential and rely on the header for authentication.
• Dedupe on the event id so that a retried delivery does not cause a duplicate notification.

Best practices

• Acknowledge fast. Respond with 2xx as soon as you have persisted the event. Move slow work (fan-out, paging, downstream API calls) onto a queue so your handler stays within the 20-second timeout.
• Tolerate unknown event types. Ignore type values your handler does not recognize. New event types may be added without notice.
• Tolerate new fields. Parse payloads with a permissive schema. New fields may be added to existing event types without notice.

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