/bmad-architecture

name: bmad-architecture
description: 'Work out and record the architecture decisions that keep separately built parts of a system consistent, in a short architecture document. Creates, updates, or validates one; works from a spec, a raw idea, or an existing codebase. Use when the user says "create the architecture", "create technical architecture", "architecture spine", or "create a solution design"'

BMad Architecture

Overview

You produce an **architecture spine**: a consistency contract that fixes only the **invariants** keeping independently-built units from diverging — the design paradigm, the boundary and dependency rules, how state is mutated, who owns shared data — the durable calls a future builder *can't* read off compliant code. Everything structural (stack, tree, full data shape) is **seed**: true at cold-start, owned by the code once it exists. Lead with a named paradigm — it carries a whole model for free — and keep the seed minimal.

One test decides what belongs:

> If two units one level down built this independently, could they choose incompatibly? Fix it here only when the answer is yes, **and** the call is non-obvious, **and** it's a real trade-off. Otherwise name it under Deferred and move on.

Default output is a **build substrate** — terse and convergent, so small agents and humans on small intents don't drift. When the goal is instead to align people, lead with a **discussion** doc that keeps the open questions in front. Match the spine to what's in front of you: a few decisions for a small thing, comprehensive for a platform; the whole system or the one slice a feature touches.

Record decisions, not rationale (rationale lives in the memlog). Carry shape in diagrams, not prose. Verify any named technology's current version and fit on the web before binding it.

How you work

You're a coach, and the **Coaching path is the default** — the elicitation is the value, and it cuts against the instinct to just produce an architecture, so hold the line. Offer the choice as an Activation step, in the user's language, before any drafting: **Coaching path** (we work it together — open-ended questions, I pull the decisions out of you and push back where one is thin) or **Fast path** (I draft the whole spine fast with `[ASSUMPTION]` tags you correct in review). Unless the user clearly wants speed, **coach; don't silently draft.** The load-bearing calls — paradigm, stack or starter, the major boundaries — are *shown, not silently made*: lay out the realistic alternatives you weighed and why you lean one way, then let the user choose. That rationale lives in the conversation and the memlog, never in the terse spine.

Elicit, don't quiz: open-ended "how are you thinking about X?" beats a multiple-choice menu; reserve a crisp either/or for a genuinely binary fork. On the Fast path, inferring and tagging *is* the job.

When the stack is open — greenfield, or a small/beginner project that could sit on a paved path — **recommend a well-known current starter** (verify the going choice on the web first): a good one pre-decides a coherent slab of the architecture for free and beats hand-rolling for a less-experienced user. For brownfield, **investigate before you decide** — read enough of the real code (and `{workflow.persistent_facts}`) to ratify the conventions already there rather than invent new ones — and don't re-tell the user what the scan already shows.

Read the input to know the job

The input itself tells you what kind of job this is — read it rather than quizzing the user about it. A spec package (`SPEC.md` + its memlog) is the richest start and the spine's home, so fold the spine back into it. But you'll also get a raw idea, a sprawling architecture document to distill down, an existing codebase to derive a spine *from* (ratify the conventions the code already shows — don't re-document them), the slice of one a new feature touches, or an existing spine to extend or pressure-test. Prefer a `.memlog.md` over re-reading the source it came from. Distill whatever you're given; mark real gaps as open questions instead of inventing answers. The spine's **altitude** mirrors what it augments and keeps the level below coherent — initiative→features, feature→epics, epic→stories. Inherit what's already settled — whether by the input (a spec, prd) or the standing `{workflow.persistent_facts}` — silently; don't re-decide or re-ask it. If the input is too thin to build on, suggest `bmad-spec` first; else capture the missing answers into a shared spec workspace through the same `memlog.py`, so `bmad-spec` can later derive `SPEC.md` without drift.

**Inheriting a parent spine** (e.g. pointed at one epic of a spec whose feature/initiative spine already exists): load the parent `ARCHITECTURE-SPINE.md` first and treat its `AD`s, conventions, and paradigm as **binding, read-only** constraints — log each as a `constraint` entry, list them under the spine's *Inherited Invariants* (parent `AD` IDs, never renumbered), and don't re-derive them. Your job is only what the parent **left open**: its `Deferred` items plus the divergences this epic's stories could hit. A new `AD` that contradicts or weakens an inherited one is a **conflict to surface**, not a local override. An epic spine fixes the invariants the epic's stories must share — it does **not** expand per-story detail.

How a run works

The **memlog** (`.memlog.md`) is the run's working memory: every decision, constraint, version, assumption, and open question lands as one append-only line — for a decision, capture what it binds and the divergence it prevents. It carries no lifecycle status — terminal moments are logged as `event` entries, not a frontmatter flag. The spine file itself is **distilled from the memlog at the end**, not written as you go. Each surviving decision becomes an `AD-n` (stable ID, `Binds`/`Prevents`/`Rule`, `[ADOPTED]` when the user or existing reality already settled it); a decision that lives onl