> For the complete documentation index, see [llms.txt](https://wiki.4thtech.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://wiki.4thtech.io/developers/sdk.md).

# 4thTech SDK (OCC v1)

What the 4thTech SDK and the BlockMail & BlockChat white-label apps are, who they are for, and their status.

{% hint style="info" %}
**Status: Maintenance mode.** The 4thTech SDK and the BlockMail & BlockChat white-label apps are supported for existing users; no new features are planned. Last release: SDK 0.5.13 (25 Nov 2025).
{% endhint %}

The 4thTech SDK is a set of TypeScript packages (`@4thtech-sdk/*`) for sending and reading encrypted mail and chat messages with OCC v1, the first-generation 4thTech protocol. The BlockMail & BlockChat white-label apps are a ready-made web app built on that SDK. (Earlier documentation called them dMail and dChat.)

Both are in maintenance mode: they are supported for existing users, and no new features are planned. For new agent-to-agent work, see [AgentLink](/products/agentlink.md), which uses OCC v2.

## Choose your path

| You want to...                                | Go to                                                                   |
| --------------------------------------------- | ----------------------------------------------------------------------- |
| Use BlockMail & BlockChat as a person         | [Get started](/products/white-label/get-started.md)                     |
| Run your own copy of the app under your brand | [Fork, configure and run locally](/products/white-label/run-locally.md) |
| Add mail or chat to your own app              | [SDK quickstart](/developers/sdk/quickstart.md)                         |
| Look up a class or method                     | [Reference for SDK 0.5.x](/developers/sdk/ethereum.md)                  |
| Understand how the packages fit               | [How the SDK fits together](/developers/sdk/how-it-fits.md)             |

## What is in the SDK

| Package                                                    | What it does                                                                     |
| ---------------------------------------------------------- | -------------------------------------------------------------------------------- |
| [`@4thtech-sdk/ethereum`](/developers/sdk/ethereum.md)     | `Mail`, `Chat`, `Encryptor` and `User` clients that talk to the OCC v1 contracts |
| [`@4thtech-sdk/encryption`](/developers/sdk/encryption.md) | An `EncryptionHandler` with AES and Encryptor-based AES encryption               |
| [`@4thtech-sdk/encryptor`](/developers/sdk/encryptor.md)   | A connector to the [Encryptor](/products/encryptor.md) browser extension         |
| [`@4thtech-sdk/storage`](/developers/sdk/storage.md)       | Remote storage providers, including PollinationX                                 |
| [`@4thtech-sdk/types`](/developers/sdk/types.md)           | Shared type declarations                                                         |
| [`@4thtech-sdk/utils`](/developers/sdk/utils.md)           | Buffer, checksum and error helpers                                               |

## What the white-label apps are

BlockMail & BlockChat is a Nuxt 3 web app. You connect a wallet, pick one of 12 networks, set up [Encryptor](/products/white-label/encryption.md) and [storage](/products/white-label/storage.md), then send mail and chat messages that only the recipient can read. You can also fork it, brand it and host it yourself.

## Who should read what

* **People who want to use the apps:** the user manual under "White-label apps".
* **Organisations that want their own branded app:** "Run your own white-label".
* **Developers:** "Developers", then the reference.

You sign every action with your own wallet. Nobody holds your keys for you. The apps and the SDK are open source; see [Licence](/developers/sdk/licence.md) and [Status](/developers/sdk/status.md).