---
title: Engineering notes | How Maro Labs builds with Claude
url: https://marolabs.kr/engineering/
language: en
alternates: ko https://marolabs.kr/ko/engineering/ ; ja https://marolabs.kr/ja/engineering/
updated: 2026-10-13
---

> How Maro Labs builds Maro Portal and Maro Writer with Claude: who does what, evidence-first rules, the seven-part definition of done, review rules, four questions before any change, model switching, and dated records.

[Home](https://marolabs.kr/) / Engineering notes

# Engineering notes: how we build with Claude

The working rules behind Maro Portal and Maro Writer, taken from Maro Portal's own operating charter and work records. Built with Claude.

## Who does what

Maro Labs is founder-led and works with parallel AI workers. The split below is how Maro Portal and Maro Writer are built every day.

- **Claude: direction, design, review**:

  Claude carries over 70% of the important work: setting direction, designing, planning, and the key reviews. Maro Writer was specified in a Claude Code session, and Claude is connected inside both apps.
- **Other AI tools: build and second review**:

  Other models, mainly OpenAI Codex, take implementation and second reviews. Who builds and who reviews are chosen separately, so the author of a change is not its only reviewer.
- **Maro: decides**:

  Maro sets the goal, approves anything that cannot be undone, and makes the final call. Decisions are kept with their original wording.

## Evidence, then analysis, then conclusion

1. **Look at the real thing first:** the running app, its state, and the original records.
2. **Separate facts from opinion** and inference.
3. **Weigh the risks and the alternatives.**
4. **Conclude only within what was shown.** A claim of PASS or done is measured again, and anything not checked is reported as not checked.

## What done means

Writing code is not done. A task is done only when all seven are in place. Something not shown at runtime is reported as code and unit tests passed, runtime not shown.

1. Implementation
2. A check that can be run or reproduced
3. Feature verification
4. Regression check
5. Evidence kept
6. Records corrected
7. An honest note of what is still limited and the next risk

## How reviews work

Every task in Maro Portal goes through a separate review before it closes. These are the rules the reviewers follow.

- **Author and reviewer apart**:

  Where possible, the worker that made a change does not review it. Numbers, hashes, files, and running state are compared directly, not taken from a report.
- **A partial pass stays partial**:

  Results from several reviewers are tied to the same scope. A partial pass is never rounded up to a full pass, and notes on a pass-with-notes are not erased.
- **Receipts name the model**:

  Every review and run receipt keeps the actual provider and model, its role, and the run it came from. Earlier results keep their original source when the model changes.
- **Reviewers by capability**:

  Review tasks are assigned by what a model can actually do (read text, see screens, run tools), not by brand. A screen a model could not see is never marked as passed.
- **No verdict shopping**:

  If a provider fails with no verdict at all (empty reply, disconnect, limit, timeout), the same input goes to the next registered reviewer. If any verdict came back, it stands until a person looks at it.
- **Reuse only current evidence**:

  An earlier review is reused only when the file paths, SHA-256 hashes, and scope still match. Changed files and what they affect are read again.

## Four questions before any change

Before a patch, an install, a settings change, a deletion, or anything sent outside, these four answers set how heavy the review is.

- **How bad if it goes wrong?**:

  The size and reach of the harm: who and what, and for how long.
- **Can it be undone?**:

  Is there a real way back: an earlier version, a copy, a restore step?
- **Is it one-way?**:

  The heaviest question. If yes, stop once more and get a copy, evidence, and Maro's confirmation first.
- **Does the whole get heavier or lighter?**:

  Before adding a new check, rule, or file, look for something to remove, merge, or fix first.

## Switching models without losing the work

Goal, scope, current state, changed files with their hashes, test results, open findings, and handoff notes live in Maro Portal's own work records, not in a model's chat session.

Changing the model does not restart the work or repeat finished steps. The switch happens at the next safe step, after the previous run is confirmed finished or cancelled.

A model the user picked is never silently replaced by another. A late result from the old model is never adopted as the new model's result.

## Work folders by month

|  |  |
| --- | --- |
| July 2026 | 41 |
| August 2026 | 51 |
| September 2026 | 308 |
| October 1–12, 2026 | 562 |

## On the record

dated work folders filed by Maro Portal, July 1 to October 12, 2026
:   962

of them are review reports
:   211

works with a review history, as of August 20, 2026
:   56

of those needed two or more review rounds (up to five)
:   24

## How the rules came to be

- **July 14, 2026**Operating charter v1 adopted for all Maro Portal work. A CLAUDE.md entry makes every Claude session read it first.
- **July 17, 2026**The charter makes Maro Portal model-independent: outside AI models are pluggable parts, not separate identities.
- **August 20, 2026**Claude independently re-reviews a strengths-and-weaknesses packet written by Codex, reading only, and records which claims it could and could not confirm.
- **September 13, 2026**Rule added: the building model and the reviewing model can each be swapped without losing the work.
- **September 27, 2026**Maro Writer specified in a Claude Code session; 309/309 regression checks pass.
- **September 30, 2026**Rule added: a provider failure does not use up a review, and verdict shopping is not allowed.
- **October 12, 2026**Rule added: four questions before any change, so small reversible changes move fast and one-way changes get a second stop.

[Changelog →](https://marolabs.kr/updates/) · [Built with Claude →](https://marolabs.kr/about/#claude)

## Want to use Maro Portal or Maro Writer?

Tell us which app and what for. We reply by email.

[Request access](https://marolabs.kr/request-access/)[FAQ](https://marolabs.kr/support/)

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Maro Labs · South Korea · founder@marolabs.kr · https://marolabs.kr/ · Built with Claude