Otel Weaver

---
name: otel-weaver
description: OpenTelemetry Weaver registry authoring, codegen, and CI enforcement. Use when adopting Weaver, authoring or reviewing a registry (manifest, attributes, metrics, spans, events), writing Jinja2 templates against the resolved schema, migrating hand-maintained telemetry constants, wiring `weaver registry check`/`generate`/`diff` into CI, or choosing a Weaver version for a semantic-conventions release.
---

# OpenTelemetry Weaver

Use this skill when an organization wants to define its own semantic conventions on top of upstream OTel and generate language bindings from them.

Usage:
- pair with `otel-semantic-conventions` to decide which attributes already exist upstream and should not be redeclared in the local registry
- latest Weaver version: the `otel-sdk-versions` index if it lists Weaver, else <https://github.com/open-telemetry/weaver/releases>; `references/ci-integration.md` keeps a dated Weaver/semconv compatibility record for offline answers

If a companion skill is unavailable:
- do not stop
- do not rely on memory alone when the guidance can be checked from official sources
- consult the Weaver repo, `schemas/semconv-syntax.v2.md`, and `docs/usage.md` / `docs/validate.md`
- state which fallback you used and leave any unverified item unresolved

## Mental Model

Three moving parts:

1. **Registry** — directory of YAML files. `manifest.yaml` is required; its `schema_url` (OTel schema URL format, `http[s]://host/path/<version>`) both names the registry and carries its version in the final path segment. Dependency entries also require `schema_url` plus optional `registry_path`. The rest declare `attributes`, `metrics`, `spans`, `events`, `entities`. The version segment of `schema_url` is yours to manage; bump it on changes. (`semconv_version` and `schema_base_url` are deprecated in favor of `schema_url`; top-level `name` is not a v0.26.1 manifest field.)
2. **Templates** — directory of MiniJinja files (Jinja2-compatible, not full Jinja2 — auto-escaping is off by default since v0.22.0 and loop `break`/`continue` are supported) plus a `weaver.yaml` per target language describing which templates to run, with what filter, in what `application_mode`, and with what output filename.
3. **Policies** — Rego rules evaluated by the Regorus (OPA-compatible) engine, in four packages: `before_resolution` (raw parsed groups; unsupported and skipped with `--v2`), `after_resolution` (resolved registry), `comparison_after_resolution` (only when `--baseline-registry` is passed), and `live_check_advice` (per-sample during `live-check`). Built-in OTel policies are the floor; custom policies layer on org rules.

These three replace a hand-rolled `const.go` (or equivalent): const blocks become the registry, the act of writing them becomes codegen, and tribal knowledge becomes policies.

## Non-Negotiable Rules

- Install Weaver via one of the methods documented at <https://github.com/open-telemetry/weaver#install> (release binary, `otel/weaver:vX.Y.Z` Docker image, or the `setup-weaver` GitHub Action). Never `brew install weaver` — that resolves to an unrelated Scribd tool.
- Reference upstream semconv attributes by `ref` rather than redeclaring them. Boundary domains (`http`, `db`, `messaging`, `rpc`, `network`, `gen-ai`, ...) belong in upstream OTel semconv, not in a local registry. Use the language SDK's semconv package for those at runtime.
- Every attribute and signal definition needs `stability`; include it on enum members too, as required by the v2 syntax guide. Weaver v0.26.1 rejects missing definition stability but reports missing enum-member stability only as a non-fatal warning in normal mode.
- In v2, an attribute reference may refine fields such as `brief`, `note`, `examples`, and `annotations`, but not `stability` or `deprecated`; those always come from the attribute definition.
- Use a domain prefix (e.g. `ecommerce.`, `acme.`) for org-local attributes, metrics, and spans.
- Run the language formatter (`gofmt -w`, `prettier`, `ruff format`, ...) on generated output. Jinja whitespace produces multiple blank lines; without formatting, the diff check in CI will fail spuriously.
- Confirm the resolved schema shape before writing a template. For a `definition/2` registry, call the grouped jq helpers with `{"v2": true}`; the v2 template `ctx` preserves fields such as attribute `key`, metric `name`, span `type`/`kind` and structured `span.name.note`, plus entity `type`/`identity`/`description`. See `references/template-authoring.md` for how to dump the exact shape.

## Workflow

1. **Install or locate Weaver.** Follow the upstream install instructions at <https://github.com/open-telemetry/weaver#install> — pick a pinned release binary, the `otel/weaver:vX.Y.Z` Docker image, or the `setup-weaver` GitHub Action. Use Docker for CI and reproducible local runs.
2. **Author the registry.** Required: `manifest.yaml` plus one or more `definition/2` YAML files declaring attributes, attribute groups, metrics, spans, events, or entities. See `references/registry-authoring.md`.
3. **Author templates.** One target dir per language under `templates/registry/<lang>/` with `weaver.yaml` plus `*.j2`. See `references/template-authoring.md`.
4. **Validate and generate.** `weaver registry check --v2 -r ./telemetry/registry/` for fast feedback. `weaver registry generate --v2 --registry ./telemetry/registry/ --templates ./telemetry/templates/ <lang> <output-dir>` for codegen. Run the language formatter on the output.
5. **Wire into CI.** Three gates: `check` (schema), `generate` + `git diff --exit-code` (checked-in code is current), `diff` against the base branch (surfaces breaking changes). See `references/ci-integration.md`.

The Weaver CLI has more subcommands than this workflow touches: `stats` and `json-schema` for quick registry sanity checks, `update-markdown` for keeping semconv snippets in docs current, `emit`/`live-check`/`infer` for working against live OTLP telemetry, `package` for writing a self-contained resolved registry artifact (the replacement for the deprecated `resolve`), `mcp` for exposing a registry to LLM tooling, and `serve` for an HTTP+UI mode. All are out of scope here (see below) but worth knowing exist before assuming `check`/`generate`/`diff` is the whole surface.

## Gotchas

These cost time and are not obvious from the upstream docs:

1. `brew install weaver` installs the wrong tool. Use GitHub releases or Docker.
2. Generated output is not formatter-clean. Always run the language formatter after `weaver registry generate`.
3. Jq helper defaults target the legacy schema. For `definition/2`, pass `{"v2": true}` and use the preserved v2 fields: attribute `key`, metric `name`, span `type`/`kind` and `span.name.note`, plus entity `type`/`identity`/`description`. Always generate and inspect the filtered `ctx` before writing a template.
4. The `comment` Jinja filter takes a keyword argument: `attr.brief | comment(format="go")`. It already emits the `// ` prefix; do not add another.
5. Attributes, metrics, spans, events, and entities all have prebuilt grouped jq filters (`semconv_grouped_attributes`, `semconv_grouped_metrics`, `semconv_grouped_spans`, `semconv_grouped_events`, `semconv_grouped_entities`). For `definition/2`, use (for example) `semconv_grouped_spans({"v2": true})` as a folded YAML scalar; the bare helper defaults select the legacy schema.
6. `weaver registry check` emits "File format `definition/2` is not yet stable" (a warning) for custom v2 definition files (still so in the dated record in `references/ci-integration.md`). This is normal; do not treat it as a failure.
7. `--future` is opt-in but still elevates the `definition/2` instability warning to an error for a custom v2 registry. Leave it off until the format goes stable.
8. CLI argument ordering for `generate`: target directory name is positional **after** `--registry` and `--templates`; the output directory follows. `--templates` points at the **parent** that contains target dirs, not at the language-specific subdir.
9. Span name in registry vs. runtime: required schema fields are `type`, `kind` (`client`/`server`/`producer`/`consumer`/`internal`), `brief`, `stability`, and a structured `name: { note: "..." }`. For internal business spans, putting the dotted type identifier in `name.note` and rendering the resolved `span.name.note` string at runtime is clean.
10. **What does NOT belong in your local registry.** DB, HTTP, messaging, RPC, network, GenAI, and similar boundary spans/attributes follow upstream OTel semconv. Until upstream is pulled in as a manifest dependency, instrumentation for those should reference the language SDK's semconv package directly. This is the most common modeling mistake.
11. Counter and UpDownCounter names should not append `_total`; this is the semconv v1.44.0 naming rule.
12. Duration instruments should use seconds (`s`) under the semconv v1.44.0 unit guidance.

## References To Load On Demand

- registry YAML field reference: `references/registry-authoring.md`
- Jinja2 patterns, jq filters, resolved-shape cheat sheet: `references/template-authoring.md`
- ready-to-lift GitHub Actions example and the dated version-compatibility record: `references/ci-integration.md`
- hand-maintained-constants → registry walkthrough: `references/migration-playbook.md`
- semantic conventions skill: `otel-semantic-conventions`
- manual instrumentation skill: `manual-instrumentation`

## Out Of Scope

These are natural follow-ups but not part of this skill:
- publishing the registry as a versioned artifact for downstream consumers (`weaver registry package`)
- declaring upstream semantic-conventions as a manifest dependency
- `weaver registry live-check`/`emit`/`infer` against live OTLP telemetry
- `weaver registry mcp` / `weaver serve`
- custom Rego policies beyond the built-ins
- helper-function codegen (`MyMetricName(meter)` wrappers)

## Verification Contract

If you authored or modified a Weaver registry, templates, or CI integration:
- re-open the changed files before finishing
- run `weaver registry check --v2` against the `definition/2` registry and capture the result
- run `weaver registry generate --v2` and the language formatter, then verify `git diff --exit-code` is clean
- confirm each applicable item with codebase evidence

Report the final check with:
- `[x]` completed
- `[~]` not applicable, with a reason
- `[ ]` unresolved

Use these items:
- registry has `manifest.yaml` with a `schema_url` whose final path segment is the version
- every definition and enum member has `stability`
- org-local attributes/metrics/spans use a domain prefix
- no boundary-domain (http/db/messaging/rpc/network/gen-ai) entries duplicated locally
- Counter and UpDownCounter names have no `_total` suffix
- duration histograms use `s` (seconds)
- templates use jq filters that match the resolved schema (for `definition/2`, call the prebuilt `semconv_grouped_*` helpers with `{"v2": true}`)
- generated output is formatter-clean
- CI runs `check`, `generate` + `git diff --exit-code`, and `diff` against the base branch
- changed files were re-read
- remaining risks or gaps are stated