> 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/home/readme.md).

# Welcome to 4thTech

Documentation for 4thTech's products, AgentLink, OCC v1, the 4thTech SDK and white-label apps, and Encryptor.

<figure><img src="https://3688459944-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZjy5DevDUBRwNkiXddc0%2Fuploads%2Fgit-blob-1328314dc93958491e6fbfb5fd6a8d589029edf4%2F4thtech-light-mode-green.png?alt=media" alt="4thTech logo"><figcaption></figcaption></figure>

4thTech builds technology for private, verifiable communication. This site documents every 4thTech product: what each one is, how to use it, how it works and what state it is in.

4thTech is developed by Block Labs S.à r.l. (Luxembourg), the licensor of the OCC v1 code. See [Licences](/home/licences.md).

## The products

### AgentLink by 4thTech

**Status: in development, nothing to install yet.**

AgentLink is designed to let your AI agent exchange messages and files with other people's AI agents, privately, and keep proof when it matters. It is being built in public: the foundations are written, and the first version you can try is planned for v0.1.0.

[AgentLink overview](/agentlink/agentlink.md) · [Status and roadmap](/agentlink/status.md)

### OCC v1 Protocol

**Status: Legacy (reference).**

The first-generation 4thTech protocol for on-chain communication: each mail, message or file handover is recorded on an EVM chain, and, with encryption on, only the people involved can read the content. Documented for existing integrations and as reference.

[OCC v1 overview](/occ-v1/occ-v1.md)

### 4thTech SDK and BlockMail & BlockChat

**Status: Maintenance mode** (supported for existing users; no new features).

A TypeScript SDK (`@4thtech-sdk/*`, last release 0.5.13 on 25 Nov 2025) for building on OCC v1, and BlockMail & BlockChat, white-label mail and chat apps you can use, fork and brand.

[SDK and white-label apps](/sdk-and-white-label/sdk.md)

### Encryptor

**Status: Maintenance mode** (supported for existing users; no new features).

A browser extension that gives web apps an encryption key, so two people can agree on a shared secret without sharing their keys. Used by BlockMail & BlockChat for end-to-end encryption.

[Encryptor](/encryptor/encryptor.md)

## Which product is for me?

| You want to…                                                                  | Go to                                                                    |
| ----------------------------------------------------------------------------- | ------------------------------------------------------------------------ |
| Let your AI agents talk to other people's AI agents, privately and with proof | [AgentLink](/agentlink/agentlink.md) (in development)                    |
| Send encrypted mail and chat messages with your Web3 account                  | [BlockMail & BlockChat user manual](/sdk-and-white-label/get-started.md) |
| Build an app on the OCC v1 contracts                                          | [SDK quickstart](/sdk-and-white-label/quickstart.md)                     |
| Run your own branded mail and chat app                                        | [Run your own white-label](/sdk-and-white-label/run-locally.md)          |
| Set up end-to-end encryption in your browser                                  | [Encryptor user manual](/encryptor/install.md)                           |
| Find a contract address                                                       | [Deployments](/home/deployments.md)                                      |

## How the products relate

```mermaid
flowchart TB
  T["4thTech"]
  subgraph G1["First generation (Legacy / Maintenance mode)"]
    V1["OCC v1 protocol (contracts on EVM chains)"]
    SDK["4thTech SDK (@4thtech-sdk/*)"]
    WL["BlockMail & BlockChat (white-label apps)"]
    ENC["Encryptor (browser extension)"]
  end
  subgraph G2["Second generation (in development)"]
    V2["OCC v2 protocol"]
    AL["AgentLink by 4thTech"]
  end
  T --> V1
  T --> V2
  V1 --> SDK
  SDK --> WL
  ENC -. "encryption key layer" .-> SDK
  ENC -. "encryption key layer" .-> WL
  V2 --> AL
  V1 -. "ideas, no shared code" .-> V2
```

*Figure: the 4thTech product family. OCC v1 and its tools are the first generation; OCC v2 and AgentLink are the second. They share ideas, not code, keys or contracts.*

In words: OCC v1 is the base of the first generation, with the 4thTech SDK built on it and BlockMail & BlockChat built on the SDK; Encryptor supplies the encryption key layer to both. OCC v2 and AgentLink are the second generation, in development. The two generations share ideas, nothing else.

More in [The product family](/home/product-family.md).