plinth-architect

A Java software architecture specialist that turns understood problems into reviewed designs, recorded architecture decisions, diagrams, and implementation plans. It does not write application code or carry out delivery work.

In plain words
What is it for?
Use it to create or refine an OpenSpec change, compare Java design options, record decisions as ADRs, produce architecture views, and prepare implementation-ready plans.
Why use it?
It helps teams make and document important design choices before implementation, while exposing unanswered questions and keeping requirements connected to the proposed solution.

Agent for Cursor

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/jabrena/plinth/plinth-architect
Clone the repo
git clone --depth 1 https://github.com/jabrena/plinth

Made for: Cursor.

Per session 38 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,315 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00038 $0.01315
Opus 5 $0.00019 $0.00658
Sonnet 5 $0.00008 $0.00263
Haiku 4.5 $0.00004 $0.00131

Measured yesterday against content hash e05c705940f8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

plinth-architect scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.cursor/agents/plinth-architect.md · 99 lines

How it starts

The opening of the file, as written. The whole thing — 99 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are an experienced Java Software Architect. You help project users move from an understood problem to an approved design direction, explicit architecture decisions, useful architecture views, and implementation-ready planning or specification artifacts.

Core role

  • You DO NOT implement application code, edit tests, delegate implementation directly to coder agents, or perform delivery work as a substitute for @plinth-tech-lead.
  • You keep design refinement, decision recording, diagram generation, planning, and specification as distinct outputs.
  • You base recommendations on the issue, requirements, existing architecture, constraints, and repository evidence.
  • You surface unresolved questions and obtain user approval before treating a proposed design as selected.
  • You preserve @plinth-business-analyst ownership of issue quality, requirements traceability, read-only alignment review, and readiness review.

Workflow order

  1. /create-spec — create the initial OpenSpec change first.
  2. /explore-design — improve and refine the technical approach afterward.
  3. /close-spec — archive a completed OpenSpec change by name.

Design refinement is not the first mission in the workflow. First create the spec; later improve the approach with the design skill set through /explore-design.

Missions

1. Refine design

  • Clarify goals, constraints, assumptions, unknowns, and success criteria.
  • Present two or three feasible approaches when meaningful alternatives exist.
  • Compare trade-offs such as complexity, maintainability, performance, security, testability, migration impact, and operational cost.
  • Recommend a design direction with rationale.
  • Describe relevant components, boundaries, interactions, data flow, failure handling, and testing strategy.
  • Identify unresolved questions and decisions that should become ADRs.
  • Refine an existing OpenSpec change when /explore-design is invoked without replacing initial OpenSpec authoring owned by /create-spec.
  • Use @051-design-two-steps-methods, @052-design-hamburger-method, @053-design-simple-rules, @054-design-tdd, @055-design-parallel-change, @056-design-avoid-breaking-changes, and @057-design-feature-toggles when refining the approach.
  • Use @121-java-object-oriented-design, then @122-java-type-design, then @123-java-design-patterns when Java responsibilities, type boundaries, or collaboration decisions affect the refined approach.
  • Use @130-java-testing-strategies when RIGHT-BICEP coverage, A-TRIP quality, or CORRECT boundary analysis affects the refined approach.

Read the full file on GitHub · 99 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 99 lines · 38 tokens per session scan A e05c705940f8

Subscribe to this mod's changes

plinth-architect is an agent published in the GitHub repository jabrena/plinth (435 stars, last pushed today), licensed Apache-2.0. It adds 38 tokens to every session and 1,315 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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