> ## Documentation Index
> Fetch the complete documentation index at: https://docs.tracelane.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# OpenTelemetry capture

> What OTLP spans retain, which fields follow the workspace content setting, and how limits are reported.

Send OTLP trace spans to the gateway's authenticated `POST /v1/traces` endpoint.
The gateway accepts OTLP protobuf and OTLP JSON. The API key identifies the
workspace; a tenant ID in the payload does not select another workspace.

## Content follows the workspace setting

In **Settings → Workspace**, the owner controls input and output capture separately.
An exporter sending text does not override that choice. Without a known workspace
choice, the workspace half is off. A gateway operator's configured capture
allowlist can also enable a half. The direct mTLS ingest receiver uses only the
workspace decision; without a control plane, it drops content and keeps metadata.

| Input capture | Output capture |
| - | - |
| Input messages and system instructions | Output messages |
| OpenInference `input.value` | OpenInference `output.value` |
| Retrieval query and document content | Model-generated tool arguments |
| Tool results fed back to the model | Evaluation explanations |

Unknown string attributes require **both** halves to be enabled. Unknown content
families, such as prompt or completion keys without a supported typed mapping,
are dropped even when capture is on. A span's `tracelane_content_withheld` field
names input/output halves that arrived and were removed; absence of that marker
does not imply the exporter sent text.

Metadata and tags are developer labels, stored independently of the content
switches. Do not put end-user text in them. Supported sources include
`tracelane.metadata.<key>` / `tracelane.tags`, OpenInference `metadata` / `tag.tags`,
and Langfuse trace metadata/tags. Values are bounded and pass through ingest redaction.

## Fields retained

The decoder maps supported OpenInference `llm.*` aliases and current OTel GenAI
attributes into model, provider, token, finish-reason and tool metadata. Canonical
GenAI attributes win over aliases regardless of their order. Tool definitions
retain names and counts; schemas are not retained. Indexed OpenInference messages
are assembled in index order and then passed through the content decision.

Resource `service.name`, `service.version` and `deployment.environment.name`
(or legacy `deployment.environment`) reach each span; span attributes take
precedence. Default unknown-service names stay absent. Other resource attributes
are dropped.

Exception events retain type, message and a bounded stack trace as metadata.
Message events fold into the input/output fields and follow their capture setting.
Links retain trace/span IDs; link attributes are dropped. Supported MCP method,
session, protocol and tool metadata are retained. Ingest redaction applies to
retained attributes before storage.

## Limits

These are the seeded defaults; operator policy can change them.

| Field | Default bound |
| - | - |
| Each retained content field | 65,536 UTF-8 bytes, including a truncation marker |
| Unknown attributes, shared across span and events | 32 keys per span |
| Unknown attribute key / string value | 128 / 256 bytes |
| Unknown scalar array | 16 items |
| Events / links / retrieval documents | 32 / 16 / 20 per span |
| Event attribute / exception stack trace | 1,024 / 16,384 bytes |

Oversized unknown strings are dropped, not truncated. Content and stack traces
are cut safely at UTF-8 boundaries; sufficiently large caps include
`…[truncated]`. Other batch, span-size and attribute-count limits still apply.
`tracelane_attrs_dropped` records dropped items by reason, including limits,
strings withheld by capture policy, unmapped content, resource keys and link attributes.

The gateway cache has a nominal 15-minute TTL; a failed refresh can retain the
last known choice longer. The direct ingest cache uses a 30-second TTL and drops
content when its policy lookup fails. Turning capture off affects new spans once
the receiving process observes the change. It does not retroactively erase
recorded text. See [Prompt content](/security#prompt-content)
for ownership, redaction and retention details.