Type one sentence. Get the architecture right — in any language.

1 · You

You type one sentence.

Open your coding agent in a project that has almost nothing in it. Type: add hexagonal architecture to this project.

That is the whole request. No folder layout, no pasted guide. Without a recipe, an agent invents its own “hexagonal” from memory, and nothing says it got it right.

Hexagonal architecture is a way to lay out code so the business rules never depend on the plumbing around them (the database, the web layer, the screen). Its inventor, Alistair Cockburn, also calls it “ports and adapters”.

2 · Your agent

Your agent asks MM3 how.

You do nothing. Your agent sends your sentence to MM3 and a recipe comes back. It even works out the language on its own, from Cargo.toml.

The one rule that matters: the business logic never reaches into the database code directly. The business rule talks only to its own socket.

The recipe is not made up. It traces to Alistair Cockburn’s own page, dated 2005-09-04. MM3 checked that the name, the date and the intent are quoted from that page. The four parts and the rules are our reading of his intent, and the recipe says so itself.

3 · Your agent

It writes the code, in your language.

Still nothing for you to do. The agent writes the files the recipe names, builds the project and runs it. It prints [("tea", 2)]: an order of two teas, saved.

The honest wrinkle. The first build failed. Cargo looks for src/main.rs, and the recipe puts main.rs at the project root. The recipe did not say so. The agent added a three-line block to your Cargo.toml and told MM3 about the gap, so the recipe can be fixed for the next person.

4 · MM3

MM3 checks it.

You say yes to one paid check (we said yes, once). The result, run MM3-0371: pass.

The check is a fixed list of 12 questions: 9 yes/no, one overall goal, two judgement calls. The panel shows three of the nine. A score is how sure the checker is that the answer is “yes”, and for these, yes is the healthy answer.

The questions are locked with a fingerprint, so nobody can reword them later to make a result come out better. The check cost about $0.00005 (estimated from tokens).

5 · Try it

Is it just saying yes? Break one line.

A check that always says yes is worthless. So we made a copy that breaks exactly one rule: the business rule reaches into the database-side code, which is exactly what the one rule forbids. We then asked the same questions again. Flip the switch to do it yourself.

Watch the marked check fall (Q2 and Q3 both do, while Q1 stays high: the rule still rejects a zero quantity). A check that is not about the broken rule mostly holds, so the check is not just shouting “fail” at everything. It starts in Rust; every score comes with its real run.

// Domain core: the order rule. It knows only the port, never an adapter.use super::ports::OrderStore;pub fn place_order(store: &mut impl OrderStore, item: &str, qty: i64) -> Result<(), String> {    if qty <= 0 {        return Err("quantity must be positive".to_string());    }    store.save(item, qty as u32);    Ok(())}

6 · Try it

Pick your language.

The same questions work in any language, because they ask about roles (the business rule, the socket, the plug, the start-up file), not one language’s syntax. The recipe finds your language from your project’s own files.

Pick one. The panel swaps in that app’s real business-rule file and the real result for it. The switch from the last step carries over, so you can see the broken copy in any language too.

7 · The result

What it comes to.

One sentence from you. A recipe from the person who named the pattern. Working code. And a verdict you can read: yes to the good copy, no to the broken one, in all six languages, naming the part that broke.