Rule proposal: Attribute keys are limited to printable Basic Latin characters in the range U+0021–U+007E.

[antonjim-te]

Proposal

Rule ID: ATTR-001

Description: Attribute keys are limited to printable Basic Latin characters in the range U+0021–U+007E.

Rationale: Limiting attribute keys to printable Basic Latin (U+0021–U+007E) ensures cross‑language and cross‑protocol interoperability, avoids control characters, whitespace, and Unicode normalization/confusable risks, and yields predictable parsing, filtering, and indexing across collectors, gateways, query engines, and storage. This reduces ingestion and serialization failures and keeps dashboards, alerts, and routing rules portable and reliable.

Target: Attribute (applies to Resource | Span | Metric | Log)

Criteria: The rule is violated if any attribute key contains a Unicode code point outside U+0021..U+007E. Equivalently, a key must match the regex: ^[!-~]+$.

Impact: Important

Type: Recommendation.

Ref: https://opentelemetry.io/docs/specs/semconv/general/naming/#recommendations-for-application-developers

[jpkrohling]

Intuitively, I'd agree, but I also like the idea of having emojis in keys :-) Have you seen this situation causing problems in the real world? Would you share more details about what happened?

[antonjim-te]

Intuitively, I'd agree, but I also like the idea of having emojis in keys :-) Have you seen this situation causing problems in the real world? Would you share more details about what happened?

Thanks for the feedback @jpkrohling ! It's true that emojis in keys could be fun, but we have seen real world issues:

We encountered a problem where some customers created an attribute with a space in its key, as our code at the time did not enforce that limitation. This led to significant issues when trying to ingest the telemetry data:

• The metrics with that attribute were ignored and not ingested in Spunk Observability cloud.
  • Spunk Observability cloud did not return an error, silently ignoring.
• Customer stopped receiving ThosuandEyes OTel telemetry data in their backend as all the metrics contains that attribute
• I have not tested in other Observability backend but that could be a potencial issue too.

Thanks :)