Spec Authoring

Spec Authoring

Overview

This skill is the agent-facing entry point to the Engineering Spec Authoring Standard: how to write engineering specifications in docs/specs/. A spec is a behavior contract (testable WHAT + WHY, linked to implementing modules), owned by Engineering / Architecture.

It has two distinct companions — keep the roles separate:

• spec-authoring (this skill) = authoring engineering specs. Scope a subsystem into a file, assign stable IDs, structure a behavior-contract document, decide granularity, run pre-spec technical research, and move a spec through its lifecycle.
• spec-linked-docs (SLD) = traceability. Keep source code in sync with the spec via docstring References and a CI checker.
• prd-authoring = product PRDs (a separate, product-owned standard — docs/prd/).

SPEC ≠ PRD. A SPEC is an engineering contract (SPEC-{SUBSYSTEM}-{NN}~{rev}, in docs/specs/, owned by Engineering). A PRD is a product requirements doc (PRD-{AREA}-{NN}, in docs/prd/, owned by Product). A spec implements a PRD requirement and cites it; product framing (problem, users, acceptance criteria, metrics) stays in the PRD. Do not put PRD content in a spec.

Full standard: docs/specs/AUTHORING.md. This skill orients and links; AUTHORING.md is the authoritative, portable standard. The ID grammar itself lives in docs/specs/README.md — defer to it; never re-derive it.

Use this skill, do not duplicate it. SKILL.md is a concise router. The detailed rules live in AUTHORING.md and the five reference files below. Read the reference you need.

When to Use

• Creating a new docs/specs/{subsystem}.md file for a subsystem.
• Adding a governed SPEC-{SUBSYSTEM}-{NN}~{rev} section to an existing spec.
• Deciding whether a behavior is one ID, several, or none.
• Deciding whether to add a new subsystem (file) or a section to an existing one.
• Running pre-spec technical research and recording it in docs/specs/research/.
• Moving a spec through its lifecycle (Draft → Review → Active → Superseded).

If your task is instead linking code to an existing spec, use spec-linked-docs. If you are authoring product requirements, use prd-authoring.

Core Model (at a glance)

A claude-mpm spec is a behavior contract: one bounded subsystem = one file (docs/specs/{subsystem}.md). Each governed section has a stable {#SPEC-{SUBSYSTEM}-{NN}~{rev}} ID and contains:

• Behavior Contract (WHAT) — Inputs / Outputs / Preconditions / Postconditions / Error conditions.
• Rationale (WHY) — design decisions and constraints (mandatory; never HOW). Cite the PRD-{AREA}-{NN} requirement realized, if any.
• Implementing Modules — the HOW-link table (SLD verifies these).

Around the governed sections sit a header block (Status, Version, Subsystem, Owner=eng, Last-updated, Related), Purpose & Scope, a Table of Contents (ID → section → modules), Open Questions / Future Work, and References.

There is no Acceptance Criteria or Success Metrics section — those are PRD concerns.

The copy-pasteable template is in references/spec-template.md.

Quick Start

1. Read the grammar. docs/specs/README.md §4 defines SPEC-{SUBSYSTEM}-{NN}~{rev} and the declaration rule. Do not invent IDs.
2. Pick or create the subsystem file. One bounded subsystem = one file. See references/category-taxonomy.md for the existing seven subsystems and the add-subsystem-vs-section rules.
3. Apply the spec template. Copy references/spec-template.md; fill the header block, Purpose & Scope, ToC, and each governed section.
4. Get granularity right. One ID per independently-verifiable behavior. Use the litmus test and split/merge heuristics in references/granularity-guide.md.
5. Cite the PRD requirement realized (if any) and your research. Non-obvious decisions link to docs/specs/research/NN-topic-slug.md. See references/research-conventions.md.
6. Link implementing modules in each section's table; engineers then add SLD References blocks (handoff to spec-linked-docs).
7. Run the CI check. uv run pytest tests/test_spec_traceability.py verifies the traceability graph. Draft sections are exempt from UNCOVERED (see README §9b).

Reference Files

Relationship to SLD and PRDs

spec-authoring is upstream of the contract; spec-linked-docs is downstream of it. You author a section here; SLD then keeps source code in sync with it via docstring References and the four-status CI checker. A ~rev bump you make on a contract change is what SLD's OUTDATED status detects.

A spec implements product requirements. The prd-authoring skill (docs/prd/) is the product-owned companion: PRDs state the problem and requirements; specs state the engineering contract that realizes them and cite the PRD-{AREA}-{NN}. Read both skills when a feature spans product intent and engineering contract.