Otel Weaver

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
• use otel-sdk-versions only for SDK package selection; Weaver versions are tracked separately at https://github.com/open-telemetry/weaver/releases

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, 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 in v0.26.1. 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 in v0.26.1. 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 current semconv v1.44.0 naming rule.
12. Duration instruments should use seconds (s) under the current 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: 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
• 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