> For the complete documentation index, see [llms.txt](https://docs.arcan.finance/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.arcan.finance/readme.md).

# Welcome

Arcan is the build guide for confidential apps on Robinhood. Contracts are written in Solidity. Amounts stay encrypted. The chain stores a handle. Coprocessors run the fully homomorphic encryption.

If you have written an ERC-20, the calls are the same shape. The amount is not a public number.

## Where to go next

* New to the system: read the [Litepaper](/litepaper.md).
* Write a first contract: follow the [Quick start](/start/quick-start.md).
* Learn the Solidity surface: start with [What is FHEVM](/solidity/fhevm.md).
* See what to ship: [What you can build](/apps/build.md).
* Build the web app: use the [Arcan SDK](/sdk/overview.md).
* See how a transfer moves: read [FHE on the host chain](/protocol/overview.md).
* Stuck on a call: [Support](/help/help.md).

## What runs where

| Piece         | Role                                                            |
| ------------- | --------------------------------------------------------------- |
| Your contract | Decides the transfer, the check, and who may open a handle      |
| Robinhood     | Records the call and stores the new handle. It does not run FHE |
| Coprocessors  | Add, subtract, and compare the ciphertext                       |
| Access list   | Names the accounts allowed to decrypt                           |

A normal `if` on a plaintext amount would leak the number. Branch with `FHE.select`.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.arcan.finance/readme.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.