Well Arch Cost

Well-Architected Cost Optimization Review

Review changes or an architecture doc against Google's Cloud Well-Architected Cost Optimization pillar. Surface risks, then ask the user to make an explicit Accept / Mitigate / Defer / Block decision per risk.

Arguments

Workflow

1. Collect Input ──► 2. Read Context ──► 3. Pillar Analysis
                ──► 4. Risk Decision Loop ──► 5. Report

Phase 1: Collect Input

If --doc <path> is set, read the document. Otherwise gather local changes:

# Staged changes (always collected)
git diff --cached

# Unstaged changes (skip if --staged-only)
git diff

# Untracked files (skip if --staged-only)
git status --porcelain | grep '^??'

If all produce empty results (or the doc is empty / missing), inform the user "Nothing to review." and exit.

Phase 2: Read Context

For each changed file (or referenced section of the doc), read the full content. Skim related context that informs cost: IaC files (instance types, storage classes, autoscaling bounds), Dockerfiles (image size), Kubernetes manifests (resource requests / limits), CI / data-pipeline configs, and any budget / tagging policy docs.

Phase 3: Pillar Analysis

Walk the 6 principles in references/cost-review-guide.md. For each principle, use the review questions to identify findings. Tag each finding with severity (Critical / Important / Nice-to-have) and an ID prefix C-:

• Critical → C-C1, C-C2, ...
• Important → C-I1, C-I2, ...
• Nice-to-have → C-N1, C-N2, ...

Phase 4: Risk Decision Loop

Read references/risk-decision-protocol.md. For every Critical and Important finding, call AskUserQuestion with the 4-option decision: Accept / Mitigate / Defer / Block. Nice-to-have findings are listed in the report without prompting. Batch up to 4 findings per AskUserQuestion call.

Capture each decision and any free-text rationale into the risk register.

Phase 5: Report

Render the report from references/report-template.md. If --file is set, write to well-arch-cost-YYYY-MM-DD-HHmm.md in the current working directory and confirm the path. Otherwise present the report inline.

The overall verdict is Hold if any Critical risk was Blocked, Proceed with caveats if any risk was Accepted or Deferred, otherwise Proceed.

Behavior Scenarios

Scenario: Git mode review with risk prompts
  Given the user has local changes
  When /well-arch-cost is invoked
  Then changes are analyzed against the 6 cost principles
  and the user is asked Accept/Mitigate/Defer/Block per Critical or Important risk
  and a report with a populated risk register is presented

Scenario: Architecture document review
  Given the user has an architecture doc at docs/architecture.md
  When /well-arch-cost --doc docs/architecture.md is invoked
  Then the document is analyzed against the 6 cost principles
  and the same risk decision loop and report flow runs

Scenario: Staged-only review
  Given the user has staged changes ready to commit
  When /well-arch-cost --staged-only is invoked
  Then only staged changes are analyzed

Scenario: Write report to file
  Given the user wants a persistent record
  When /well-arch-cost --file is invoked
  Then the report is written to well-arch-cost-YYYY-MM-DD-HHmm.md
  and the file path is confirmed

Scenario: All risks accepted
  Given findings exist and the user selects Accept for every risk
  When the report is rendered
  Then the verdict is "Proceed with caveats"
  and each accepted risk is captured in the risk register

Scenario: One risk blocked
  Given the user selects Block on at least one Critical finding
  When the report is rendered
  Then the verdict is "Hold"

Scenario: Nothing to review
  Given no local changes and no --doc argument
  When /well-arch-cost is invoked
  Then the user is told "Nothing to review." and the skill exits

References

• references/cost-review-guide.md — 6 cost principles with focus, review questions, output format, and severity guidance per principle
• references/risk-decision-protocol.md — how to drive AskUserQuestion per risk and capture decisions into the register
• references/report-template.md — exact markdown format including the risk register and overall verdict