trace-spec-author

Builds a per-feature trace specification document. The spec is canonical input for: (a) implementation review during code review, (b) trace-shape regression tests via opentelemetry-trace-assertions and jaeger-trace-tests, (c) onboarding for new team members.

When to use

• Starting observability for a new feature.
• Auditing existing instrumentation that grew organically.
• Pre-incident-review prep (spec gaps explain why a debugging session was painful).

Step 1 - Spec template

Save under docs/observability/<feature>.md:

# Trace Spec: <Feature>

**Owner:** team-checkout
**Status:** active | draft | deprecated
**Last reviewed:** YYYY-MM-DD
**Implementations:** orders-svc 1.4+, payments-svc 2.1+

## Root span

| Field | Value |
|---|---|
| name | `order.create` |
| kind | `INTERNAL` |
| status semantics | OK on 2xx, ERROR on 4xx + 5xx |

### Required attributes

| Attribute | Type | Source | Notes |
|---|---|---|---|
| `order.id` | string | UUID v4 | |
| `order.item_count` | int | int.between(1, 1000) | |
| `customer.id` | string | low-cardinality hash, never PII | |

## Child spans

### `db.query` (when persisting order)

| Field | Value |
|---|---|
| name | `db.query` |
| kind | `CLIENT` |
| parent | `order.create` |

Attributes per [OpenTelemetry DB semantic conventions]:

| Attribute | Type | Notes |
|---|---|---|
| `db.system` | string | "postgresql" |
| `db.operation` | string | "INSERT" |

### `payments.charge` (cross-service)

| Field | Value |
|---|---|
| name | `payments.charge` |
| kind | `CLIENT` (in orders-svc); peer is `SERVER` in payments-svc |
| parent | `order.create` |

Attributes:
- `payment.amount_cents` (int)
- `payment.currency` (string, ISO 4217)
- per [OpenTelemetry HTTP semantic conventions]: `http.request.method`, `url.full`, `http.response.status_code`

## Status mapping

| Outcome | Span status | Notes |
|---|---|---|
| Success (2xx) | OK | |
| Validation error (4xx) | UNSET on server side; ERROR on client side | Per [HTTP semantic conventions] |
| Server error (5xx) | ERROR | Always |

## Required test assertions

- [ ] root span name == `order.create`
- [ ] root span has all required attrs
- [ ] `db.query` is child of root
- [ ] `payments.charge` is child of root
- [ ] On 5xx from payments, `payments.charge.status == ERROR` AND `order.create.status == ERROR`
- [ ] `payment.amount_cents` always set when payment succeeds

## Change log

| Date | Change | Reviewer |
|---|---|---|
| 2026-04-01 | Initial spec | @reviewer |
| 2026-04-15 | Added `customer.id` low-cardinality req | @reviewer |

Step 2 - Map to OpenTelemetry semantic conventions

For each span, decide:

1. Is there a SemConv-defined span type (HTTP, DB, messaging, FaaS, RPC)? Use SemConv attribute names - never invent parallels.
2. Is the span domain-specific (e.g., order.create)? Use a namespaced name + custom attributes (e.g., order.id, order.item_count).

Per the OpenTelemetry HTTP semantic conventions, required attributes for HTTP client spans: http.request.method, url.full, server.address, server.port, http.response.status_code, error.type (conditionally).

Step 3 - Status semantics

Decide per outcome (referenced in your test spec):

HTTP outcome	Server span	Client span
1xx, 2xx, 3xx	UNSET	UNSET
4xx	UNSET	ERROR
5xx	ERROR	ERROR

Per the OpenTelemetry HTTP semantic conventions: "Status remains unset for 1xx, 2xx, and 3xx responses unless additional errors occurred. For 4xx codes, status stays unset on servers but should be set to Error on clients. All 5xx responses should be marked as Error."

Step 4 - Anti-cardinality rules (mandatory)

The spec MUST flag attributes that risk cardinality explosion in your observability backend:

Risk	Example	Mitigation
User ID as attribute → unbounded series	user.id: 123e4567-...	Hash to bucket OR put in span events instead
URL with query params	url.full includes raw ?token=...&id=999	Use http.route for low-cardinality template
Free-text error message	error.message: "User 123 …"	Use error.type enum + log line for detail

Add to spec: **High-cardinality attributes:** none / [list].

Step 5 - Drive tests from spec

Each "Required test assertion" in Step 1 maps to one test in opentelemetry-trace-assertions (in-process) or jaeger-trace-tests (cross-service):

def test_order_create_required_attrs():
    with use_tracer():
        create_order(items=[item])

    spans = memory_exporter.get_finished_spans()
    root = next(s for s in spans if s.name == "order.create")

    # Per trace-spec.md required attrs
    assert "order.id" in root.attributes
    assert isinstance(root.attributes["order.item_count"], int)
    assert "customer.id" in root.attributes
    # PII protection: must not contain raw email
    assert "@" not in root.attributes["customer.id"]

The spec ↔ test ↔ implementation triangle is the value: any drift between any two surfaces.

Step 6 - Change-management process

Lock in a process:

• Spec changes require a PR review by the spec owner.
• Backwards-incompatible changes (renaming order.id → order_id) require: (a) emit both during transition, (b) update consumers, (c) remove old after observation period.
• Each spec has a Last reviewed date; quarterly review enforced via CODEOWNERS or a calendar nudge.

Step 7 - Spec catalog

Maintain docs/observability/INDEX.md:

| Feature | Spec | Owner | Status |
|---|---|---|---|
| Order create | order-create.md | @team-checkout | active |
| User signup | user-signup.md | @team-identity | active |
| Refund flow | refund.md | @team-payments | draft |

Anti-patterns

Anti-pattern	Why it fails	Fix
Spec lives in Confluence/Notion only	Drifts from code; not version-controlled	Repo-resident markdown (Step 1)
Spec uses prose ("emits a span when order is created")	Ambiguous; can't drive tests	Tabular required attrs + assertions (Step 1, Step 5)
Spec invents attribute names parallel to SemConv	Two ways to ask "what HTTP method"; analytics break	Use SemConv (Step 2)
Skip cardinality review	Bills surge from per-user spans	Mandatory cardinality section (Step 4)
No status semantics	Each implementer decides; alerts fire inconsistently	Status table (Step 3)

Limitations

• This skill is a process artifact, not a code template. Adapt the template fields to your domain.
• Spec discipline requires team buy-in; one team's spec doesn't enforce another team's instrumentation.

References

• OpenTelemetry traces concept docs - span model, kind, status
• OpenTelemetry HTTP semantic conventions - required HTTP attrs
• OpenTelemetry DB semantic conventions - required DB attrs (consult docs site for current page)
• opentelemetry-trace-assertions, jaeger-trace-tests - sister skills that enforce spec conformance