> For the complete documentation index, see [llms.txt](https://docs.coti.io/coti-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.coti.io/coti-documentation/privacy-on-demand/contract-patterns-checklist.md).

# Contract patterns checklist

Use this checklist before deploying a production PoD contract. For conceptual background, see [Architecture and main components](/coti-documentation/privacy-on-demand/architecture-and-components.md) and [Async private operations](/coti-documentation/privacy-on-demand/async-private-operations.md).

## Recommended contract shape

1. Inherit from `PodLib` (primitive path) or `InboxUser` (custom path).
2. Add a network preset mixin such as [`PodUserSepolia`](https://github.com/coti-io/coti-contracts/blob/main/contracts/pod/mpc/PodUserSepolia.sol) or [`PodUserFuji`](https://github.com/coti-io/coti-contracts/blob/main/contracts/pod/mpc/PodUserFuji.sol) — presets auto-wire inbox and COTI routing in their constructor.
3. Accept private values as `it*` on EVM entrypoints.
4. Submit via `PodLib` helpers (e.g. `add64`, `gt256`) or `IInbox.sendTwoWayMessage{value: ...}(..., callbackFeeLocalWei)`.
5. Store `requestId` correlation state.
6. Implement success and error callbacks with `onlyInbox`.
7. Decode callback data into `ct*` and persist.
8. Expose status/result readers for async UX.

Preset wiring (`PodLib` + `PodUserSepolia` / `PodUserFuji`): [Reference: PodLib primitives](/coti-documentation/privacy-on-demand/reference-podlib-and-primitives.md).

## Fee and gas checklist

* Expose **payable** entrypoints when using two-way sends; forward **`msg.value`** as the total fee and pass explicit **`callbackFeeLocalWei`**.
* Call **`calculateTwoWayFeeRequiredInLocalToken`** on the deployed Inbox before production sends (see [How do PoA fees work?](/coti-documentation/privacy-on-demand/how-poa-fees-work.md)).
* Test **too-low total** and **too-low callback** reverts in addition to the happy path.

## Critical security controls

* Access-control any method that changes routing or configuration.
* Gate any call path that invokes `configureCoti(...)`.
* Keep callback handlers `onlyInbox`.
* In custom COTI flows, verify `inboxMsgSender()` matches the expected peer contract.
* Avoid external calls before state updates inside callback handlers.

## ABI correctness checklist

* Selector in `MpcAbiCodec.create(...)` matches the COTI-side target function.
* `.addArgument(...)` order matches COTI parameter order.
* Callback `abi.decode(...)` tuple matches COTI `abi.encode(...)` exactly.
* Add regression tests when callback tuple schema changes.

## Async robustness checklist

* Request starts as `PENDING` and transitions to a terminal state.
* Unknown or duplicate callback handling is defined.
* Errors are observable (`requestId`, error code, message).
* Frontend can query status by request ID (see [`PodRequest`](/coti-documentation/privacy-on-demand/typescript-pod-sdk.md)).

## Privacy and type checklist

* No plaintext sensitive values in EVM storage.
* No `gt*` in EVM public interfaces.
* `ct*` used for user-decryptable outputs.
* Type width consistency preserved through the full flow (see [Reference: data types](/coti-documentation/privacy-on-demand/reference-data-types.md)).

## Observability checklist

* Emit request-created event with indexed `requestId`.
* Emit completion and failure events.
* Index `MessageSent` on the Inbox for off-chain correlation (compact event carries `requestId` in indexed topics).

## Testing checklist

* Success callback updates expected state.
* Non-Inbox callback call reverts.
* Error callback updates failure state.
* Request ID mapping is deterministic.
* Frontend integration decrypts returned ciphertext correctly.
* Fee sufficiency: success with estimated fees plus buffer; reverts when under-funded.

## See also

* [Reference: examples and contracts](/coti-documentation/privacy-on-demand/reference-examples-and-contracts.md)
* [Contract patterns in custom logic tutorial](/coti-documentation/privacy-on-demand/tutorial-custom-logic.md)
* [Cookbook: private investor allocations](/coti-documentation/privacy-on-demand/cookbook-private-investor-allocations.md)


---

# 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 by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.coti.io/coti-documentation/privacy-on-demand/contract-patterns-checklist.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

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.