> For the complete documentation index, see [llms.txt](https://docs.trac.network/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.trac.network/documentation/developers/mainnet/dapp-developer-guide/introduction.md).

# Introduction

### What are MSB and `trac-peer`?

#### MSB (Main Settlement Bus)

**MSB is the base network** that provides:

* transaction ordering / global log
* fee + anti-spam rules
* “finality” (confirmed/signed state)

If you want anything to be considered “settled on Trac”, it must exist in MSB confirmed state.

#### `trac-peer`

`trac-peer` is the **application layer**.

Each `trac-peer` instance runs (and participates in) a **subnet**: a smaller P2P network that:

* replicates its own ordered log
* executes a deterministic Contract locally on each node
* exposes RPC so wallets/dApps can interact with that Contract

In short: **MSB settles**, and **trac-peers run the apps/contracts**.

***

### What is a subnet (in one paragraph)

`trac-peer` runs a **subnet**: a smaller peer-to-peer network that maintains an ordered log and derives a deterministic application state from it (a contract/state machine).

For economic finality and anti-spam rules, transactions are **settled on MSB** (Main Settlement Bus). Subnet nodes only execute contract operations locally once they can prove the referenced transaction exists in MSB confirmed state.

***

### Who are you? (choose your path)

#### “I just want to run it locally”

Start with:

* [Quickstart](/documentation/developers/mainnet/dapp-developer-guide/quickstart.md)
* [Bootstrap checklist](/documentation/developers/mainnet/dapp-developer-guide/bootstrap-checklist.md) (canonical step-by-step)

#### “I want to run an RPC endpoint for wallets/dApps”

Start with:

* [RPC](broken://pages/PX3IMNof4JZz5LvB71MB)
* [Production notes](/documentation/developers/mainnet/dapp-developer-guide/production-notes.md) (ops/security notes)

#### “I want to build an app/contract on trac-peer”

Start with:

* [App dev](/documentation/developers/mainnet/dapp-developer-guide/app-dev.md)
* [Intercom example](/documentation/developers/mainnet/dapp-developer-guide/references-examples/intercom.md) (real project example)

***

### Core concepts (minimal)

* **MSB (Main Settlement Bus)**: the settlement layer. Transactions become “real” when MSB confirms them.
* **Subnet**: the P2P application layer. A subnet has:
  * a discovery **channel** (`--subnet-channel`)
  * a bootstrap/join-code **bootstrap** (`--subnet-bootstrap`, 32-byte hex)
* **Protocol**: defines how user commands map into typed ops: `{ type, value }`.
* **Contract**: deterministic state machine that executes those typed ops and writes state under `app/...`.
* **Operator vs client**:
  * operator uses CLI (admin/writer/indexer/chat/deploy)
  * client (wallet/dApp) uses RPC (schema/context/state/tx submit when enabled)

***

### One “golden” mental model

When a user “calls a contract function” they are not invoking code remotely.

Instead:

1. a client prepares a typed command `{ type, value }`
2. the wallet signs the transaction hash (MSB operation `type = 12`)
3. the peer broadcasts it to MSB (fees apply)
4. once MSB confirms it, the subnet appends a reference op
5. every subnet node executes the same contract logic locally and derives the same state

***


---

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