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Expand metric instrument name allowed characters to support Windows performance counter names #5092

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Expand metric instrument name allowed characters to support Windows performance counter names #5092

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8b9e4c4
Relax metric instrument name syntax to allow any UTF-8
cijothomas May 13, 2026
b523238
Address review: forbid whitespace-only names; require BMP support
cijothomas May 13, 2026
e0d306b
Remove incorrect Prometheus leading-char-drop claim
cijothomas May 13, 2026
2b6e4a1
Clarify whitespace restriction is ASCII-only
cijothomas May 13, 2026
023d60a
Pivot to incremental allowlist expansion per review feedback
cijothomas May 14, 2026
5680b43
Expand allowlist to cover Windows perf counter names
cijothomas May 14, 2026
7c6bae2
Restrict space to non-leading/non-trailing positions per @reyang feed…
cijothomas May 14, 2026
ef6d971
Add # to allowlist for .NET CLR perf counter coverage
cijothomas May 14, 2026
8b88e67
Merge branch 'main' into cijothomas/relax-instrument-name
cijothomas May 14, 2026
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9 changes: 9 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -16,6 +16,15 @@ release.

### Metrics

- Expand the metric instrument name allowed character set to include `:`,
`\`, `(`, `)`, `%`, `*`, `#`, and space (with space restricted to
non-leading, non-trailing positions), and drop the requirement that the
first character be alphabetic. This enables Windows performance counter
style names (e.g. `\Processor(_Total)\% Processor Time`,
`\.NET CLR Memory(*)\# Bytes in all Heaps`). ASCII, case-insensitivity, and
the 255-character maximum are unchanged.
([#4371](https://github.com/open-telemetry/opentelemetry-specification/issues/4371),
[#4736](https://github.com/open-telemetry/opentelemetry-specification/issues/4736))
- Add in-development `Bind` API to synchronous instruments.
([#5050](https://github.com/open-telemetry/opentelemetry-specification/pull/5050))
- Stabilize sections of Prometheus Metrics Exporter.
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13 changes: 7 additions & 6 deletions specification/metrics/api.md
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Expand Up @@ -205,17 +205,18 @@ The instrument name syntax is defined below using the [Augmented Backus-Naur
Form](https://datatracker.ietf.org/doc/html/rfc5234):

```abnf
instrument-name = ALPHA 0*254 ("_" / "." / "-" / "/" / ALPHA / DIGIT)
instrument-name = NAME-CHAR [0*253(NAME-CHAR / " ") NAME-CHAR]

ALPHA = %x41-5A / %x61-7A; A-Z / a-z
DIGIT = %x30-39 ; 0-9
NAME-CHAR = ALPHA / DIGIT / "_" / "." / "-" / "/" / ":" / "\" / "(" / ")" / "%" / "*" / "#"
ALPHA = %x41-5A / %x61-7A; A-Z / a-z
DIGIT = %x30-39 ; 0-9
```

* They are not null or empty strings.
* They are case-insensitive, ASCII strings.
* The first character must be an alphabetic character.
* Subsequent characters must belong to the alphanumeric characters, '_', '.', '-',
and '/'.
* Characters must be ASCII alphanumeric or one of: `_`, `.`, `-`, `/`, `:`,
`\`, `(`, `)`, `%`, `*`, `#`, or space. The first and last characters MUST
NOT be a space.
* They can have a maximum length of 255 characters.

#### Instrument unit
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