reverse-engineering-saas

RES: Reverse Engineering SaaS

Turn a SaaS product into a build kit your team or your coding agent can ship.

Study a web product through the browser, document how it works, and hand off everything needed to rebuild and launch it, without touching production data.

Quick start · How RES works · What you get · Examples · Safety model · FAQ · Documentation

claude plugin marketplace add alextnetto/res

[!IMPORTANT] RES drives a real browser on accounts you control. Use it only on products you are allowed to study, read the safety model before the first run, and prefer a trial account in a separate browser profile.

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Want to rebuild a product your team relies on, or launch a competitor in your market? Ask your agent to study it with RES. The agent explores the product in a test environment, records every change it makes, and writes what it learns to files: screens and states, business rules with evidence, the data model, API shapes, design tokens, and what could stop the clone from launching, such as integrations that need approval, licenses and certifications.

At the end you get two files. REPORT.html is the report you read: one page that starts with the overview and the decisions you need to make, then walks through what the product does, every screen and rule, the data model and design, the build plan, and what to prepare before launch. The zip is for your coding agent: unzip it, give it the folder, and it starts from BUILD.md.

RES is one agent skill with plain Markdown templates and a few dependency-free Node.js scripts. It adds about 130 tokens to every session and about 4,600 when it runs (measured with claude plugin details).

Quick start

Install

In a terminal:

claude plugin marketplace add alextnetto/res

claude plugin install res@res

Inside a Claude Code session, the same commands are /plugin marketplace add alextnetto/res and /plugin install res@res. Start a new session afterwards.

For other agents that read skills from disk, copy the skill folder where your agent reads skills:

git clone https://github.com/alextnetto/res.git && mkdir -p ~/.claude/skills && cp -R res/skills/reverse-engineering-saas ~/.claude/skills/

You need Node.js 22 or later and an agent that can drive a browser and run JavaScript in the page: Claude in Chrome, Playwright MCP or Chrome DevTools MCP.

Prepare a safe environment

Create a trial account of the product with an email you own, log in to it in a separate Chrome profile, and connect your agent's browser tool to that profile (how). This is the safest setup: the agent cannot reach your production account even by mistake.

Without a trial account, the agent writes only if you ask it to test or to create a test environment, and then only inside a separate workspace or a sandbox container. Otherwise it only observes.

Ask your agent

Study Pipedrive so my team can rebuild it for the Brazilian market.
Use the trial profile, and don't ask me anything until you're done.

Replace the product, the market and the scope with your own. The agent creates re-<product>/ in its working directory, works through the phases below, and sends you REPORT.html and re-<product>-handoff-<date>.zip when it finishes. To continue later, start a session in the same directory and say "Continue the Pipedrive study."

Use the scripts directly

The scripts work without an agent, for example to inspect or repackage a knowledge base:

node skills/reverse-engineering-saas/scripts/init-kb.mjs --product "Acme CRM" --git

node skills/reverse-engineering-saas/scripts/check-kb.mjs re-acme-crm

node skills/reverse-engineering-saas/scripts/build-report.mjs re-acme-crm

node skills/reverse-engineering-saas/scripts/pack-kb.mjs re-acme-crm

Each script prints its options with --help.

Update

claude plugin marketplace update res

claude plugin update res@res

How RES works

flowchart LR
    A[Charter] --> B[Safe environment<br/>and preflight]
    B --> C[Public docs<br/>and barrier scan]
    C --> D[Map screens]
    D --> E[Deep dive<br/>one feature at a time]
    E -->|next feature| E
    E --> F[Synthesis:<br/>PRD, parity, barriers]
    F --> G[Close:<br/>report and zip]

The knowledge base on disk is the agent's only memory, so a study can span many sessions and survive context limits. Every statement carries its evidence: [obs] seen in the product, [net] captured on the network, [doc] from public documentation, [inf] an inference with an open question.

What you get

A rule:

### R-014 Completing the last open activity prompts for the next one
- Given a deal with exactly one open activity
- When the user marks that activity done
- Then a "Schedule next activity" dialog opens; Cancel closes it and the deal shows a warning icon
- Evidence: [obs EV-031, EV-032]

A production barrier:

### BR-003 WhatsApp messages need Meta busin