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by alextnetto
Agent skill to reverse engineer a SaaS product through the browser into a knowledge base for rebuilding it: screens, rules, data model, design tokens and production barriers, without touching production data.
# Add to your Claude Code skills
git clone https://github.com/alextnetto/resSee how res compares with popular alternatives.
res is an open-source ai agents skill for AI coding assistants such as Claude Code, Codex CLI, and ChatGPT, built by alextnetto. Agent skill to reverse engineer a SaaS product through the browser into a knowledge base for rebuilding it: screens, rules, data model, design tokens and production barriers, without touching production data. It has 72 GitHub stars.
res's catalog security scan is still queued. You can run an instant dependency and prompt-injection check now with the "Scan for vulnerabilities" button above.
Clone the repository with "git clone https://github.com/alextnetto/res" and add it to your Claude Code skills directory (see the Installation section above).
res is primarily written in JavaScript. It is open-source under alextnetto on GitHub, so you can review or fork the full source.
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Available after the catalog security scan passes.
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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.
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).
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.
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.
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."
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.
claude plugin marketplace update res
claude plugin update res@res
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]
| Phase | What happens |
|---|---|
| 1 Charter | Goal, scope, priorities and the clone's target market |
| 2 Environment | Pick the safest environment; check for automations, webhooks and integrations that could fire |
| 3 Recon | Public docs, API reference, pricing, integrations list and terms, read with web fetch; first barrier scan |
| 4 Map | Every screen and route; stack and design tokens |
| 5 Deep dive | One feature at a time: fixtures, states, rules, persistence, network, written to disk before the next feature |
| 6 Synthesis | Data model, design tokens, barriers, PRD, parity tests |
| 7 Close | Restore what changed, pass check-kb, send REPORT.html and the handoff 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.
| Area | What the knowledge base contains | Where |
|---|---|---|
| Inventory | Feature tree, screen catalog with URL patterns, a coverage matrix that works as the queue | inventory/ |
| UX | Anatomy, states (empty, loading, error, no permission, plan-gated), interactions, keyboard, accessibility, microcopy | screens/, components/ |
| Behavior | Business rules as Given/When/Then with evidence, user flows, cross-cutting topics | rules/, flows/, topics/ |
| Data | Entities with fields, enums and relations, ER diagram, TypeScript types, permissions matrix | data-model/ |
| API | Endpoint templates per user action, with JSON shapes and no values | api/ |
| Design | Color, type, spacing, radius, shadow and motion tokens, mapped to the product's CSS variables | design/ |
| Production barriers | Integrations that need approval, licenses, certifications, distribution gatekeepers and moats, with severity, market weight, lead time and mitigation | clone/barriers.md |
| Build plan | Requirements, parity tests derived from the rules, what to copy, avoid and improve | clone/ |
| Report | REPORT.html: one self-contained page a person reads, with images embedded and every ID linked |
KB root |
| Handoff | BUILD.md, a brief for any coding agent: read order, rules as tests, what not to copy |
zip root |
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 business verification
- Category: permissioned integration
- Blocks: F-014 (WhatsApp notifications)
- Gatekeeper: Meta, WhatsApp Business Platform
- Severity: blocks feature
- Market weight: required to sell
- Lead time and cost: [doc SRC-021]
- Mitigation: start verification in month one; launch with email notifications
- Evidence: [doc SRC-021]
Two end-to-end studies, run by Claude Code with Claude in Chrome without a person at the keyboard:
| Product | Environment | Result | Read |
|---|---|---|---|
| ClickUp: board, task view, custom fields | L2, a new free workspace | 55 rules, 19 components, 14 production barriers | Report · Knowledge base |
| Pipedrive: pipeline, deals, next-activity rule, won and lost | L3, a sandbox pipeline in a production account, removed at the end | 46 rules, 8 components, 15 production barriers | Report · Knowledge base |
Each folder is the unzipped handoff. Notes on trademarks and terms: examples/README.md.
| Level | Environment | What the agent may change |
|---|---|---|
| L1 | Trial account in a separate browser profile, created by you | Everything except outbound and irreversible actions |
| L2 | New, empty workspace under your login | Test data and configuration inside that workspace |
| L3 | One sandbox list, project or pipeline inside production | Test data inside the container only |
| L4 | Production, observe only | Nothing |