Architecture intelligence for AI coding agents.
Open knowledge. Open reasoning. Open architecture.
Ask a coding agent to "design a scalable API" and you will usually get Kubernetes, Kafka, Redis and three microservices — for a product with 100 users and one developer.
The agent learned the aesthetics of system design from conference talks and blog posts, drawn almost entirely from the largest 0.1% of systems. It did not learn the economics.
100 users at 40 requests per session is 0.28 requests per second. A single instance has four orders of magnitude of headroom. OAB computes that, says so, and names the exact measurement that would change the answer.
| Command | |
|---|---|
/oab:design |
Design a system proportional to its measured scale |
/oab:review |
Review this repository's architecture, weighted by what it actually runs at |
/oab:capacity |
Capacity planning with reproducible arithmetic |
/oab:adr |
Record a decision with measurable revisit triggers |
Plus a background skill that improves ordinary architecture conversation, not only explicit commands.
⚠️ Pre-release. Everything below is built and the manifest validates, but a clean-machine install has not been verified yet — #43.
/plugin marketplace add mhayk/oab
/plugin install oab@oab
From examples/tiny-startup/ — 100 users, £50/month, two developers:
## Complexity: 4 / 4 — no headroom
| Component | Kind | Cost | Why |
| Application instance | application-runtime | 1 | 0.28 peak RPS against a single |
| | | | instance leaves ~4 orders of magnitude |
| | | | of headroom. |
| Managed relational database | relational-database | 1 | 0.66 GB/year. Managed for tested |
| | | | point-in-time recovery, which a |
| | | | two-person team will not build. |
What was rejected, and when to revisit
cache— At 0.24 peak reads/second there is no measured read pressure to relieve. Revisit when: a single query exceeds 10 requests/second at over 50 ms, or database CPU is sustained above 60% for 3 days.
orchestration-platform— Three times the complexity budget and four times the money budget for a system with four orders of magnitude of headroom on one instance. Revisit when: more than 4 independently deployable services exist and a dedicated operations engineer is on the team.
That second section — what was considered, refused, and the measurement that reverses it — is the part a generic assistant never produces.
Every component costs complexity points, and every team has a budget:
available = 4 + 1.5 × (engineers − 2) + 4 × dedicated_ops
Two developers get 4 points. A managed database costs 1; a self-managed orchestration platform costs 4. Over budget is rejected by default, and an override must name what is being dropped or who will operate the excess.
At roughly £240 per point per month in engineering attention, self-hosting a database to save £250/month costs about £720/month. The managed service is cheaper — and OAB says so with arithmetic rather than preference.
It is a calibrated heuristic, not a law, and the output says that too.
Every claim OAB makes is about behaviour, and behaviour claims without tests are marketing.
| Scenarios passing | 5 / 5 |
| — overengineering guards | 3 / 3 |
| — underengineering guards | 2 / 2 |
| Calculator tests | 43 |
| Schema fixtures (both directions) | 33 |
| Knowledge units | 37 |
Assertions run against artifact fields, never prose — a framework can be tuned to produce reassuring words far more easily than the right structure. Scenarios are also perturbed 100× and 0.01× to prove they respond to magnitude rather than recognising specific numbers.
Scenario 07 is "nothing needs to change", and scenario 08 is "these requirements are inconsistent". Those are the answers an eager assistant never gives.
Honest list: no live-agent example output · no MCP server · no knowledge graph generation · no
second integration · /oab:evolve and the other nine commands are M2 · no website beyond a landing
page · 6 knowledge domains, not 18.
See ROADMAP.md, and §32 of the design for a critique of our own founding brief.
The highest-value contribution is architecture knowledge, and it requires no understanding of the codebase — copy a template, fill it in, open a pull request.
→ docs/contributing/knowledge.md
Engine, integrations and evaluation: CONTRIBUTING.md.
Apache-2.0. The OAB name and logo are trademarks and are not covered by that licence — see NOTICE.