> ## Documentation Index
> Fetch the complete documentation index at: https://docs.portalhq.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Chain ID formatting

In the world of blockchain technology, it's common to encounter different formats for representing chain IDs. While the traditional EVM chain ID format, like `1` for Ethereum mainnet, is widely recognized, [the CAIP-2 format](https://github.com/ChainAgnostic/CAIPs/blob/main/CAIPs/caip-2.md) offers a more comprehensive way to denote chain IDs across multiple curves. **At Portal, we primarily use the CAIP-2 format for chain IDs for this reason.** This document will clarify the differences and provide examples for Ethereum, Solana, and other EVM chains.

### Traditional EVM Chain ID Format

The traditional EVM chain ID format is a straightforward numerical representation used by Ethereum Virtual Machine (EVM) compatible chains. Here are some examples:

* **Monad**: `143`
* **Ethereum**: `1`
* **Optimism**: `10`
* **Polygon**: `137`
* **Arbitrum**: `42161`

### CAIP-2 Chain ID Format

The CAIP-2 ([Chain Agnostic Improvement Proposal 2](https://github.com/ChainAgnostic/CAIPs/blob/main/CAIPs/caip-2.md)) format provides a more structured way to represent chain IDs, including the namespace and reference, which helps in uniquely identifying different blockchain networks. The format is `namespace:reference`.

#### Examples:

* **Monad**: `eip155:143`
* **Solana:** `solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp`
* **Ethereum**: `eip155:1`
* **Optimism**: `eip155:10`
* **Polygon**: `eip155:137`
* **Arbitrum**: `eip155:42161`
* **Tron:** `tron:mainnet`
* **Stellar:** `stellar:pubnet`
* **Bitcoin:** `bip122:000000000019d6689c085ae165831e93-p2wpkh`

<Note>
  The only exception to our chains adhering to the CAIP-2 standardized format is Bitcoin networks, which require special consideration due to the variety of address types they support.
</Note>

### Conversion Table

<table>
  <thead>
    <tr>
      <th width="244.984375">Chain</th>
      <th>CAIP-2 Format</th>
    </tr>
  </thead>

  <tbody>
    <tr>
      <td>Monad Mainnet</td>
      <td><code>eip155:143</code></td>
    </tr>

    <tr>
      <td>Monad Testnet</td>
      <td><code>eip155:10143</code></td>
    </tr>

    <tr>
      <td>Solana Mainnet</td>
      <td><code>solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp</code></td>
    </tr>

    <tr>
      <td>Solana Devnet</td>
      <td><code>solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1</code></td>
    </tr>

    <tr>
      <td>Ethereum Mainnet</td>
      <td><code>eip155:1</code></td>
    </tr>

    <tr>
      <td>Optimism</td>
      <td><code>eip155:10</code></td>
    </tr>

    <tr>
      <td>Polygon</td>
      <td><code>eip155:137</code></td>
    </tr>

    <tr>
      <td>Arbitrum</td>
      <td><code>eip155:42161</code></td>
    </tr>

    <tr>
      <td>Base</td>
      <td><code>eip155:8453</code></td>
    </tr>

    <tr>
      <td>Base Sepolia</td>
      <td><code>eip155:84532</code></td>
    </tr>

    <tr>
      <td>Celo</td>
      <td><code>eip155:42220</code></td>
    </tr>

    <tr>
      <td>Celo Alfajores Testnet</td>
      <td><code>eip155:44787</code></td>
    </tr>

    <tr>
      <td>Stellar</td>
      <td><code>stellar:pubnet</code></td>
    </tr>

    <tr>
      <td>Stellar Testnet</td>
      <td><code>stellar:testnet</code></td>
    </tr>

    <tr>
      <td>Tron</td>
      <td><code>tron:mainnet</code></td>
    </tr>

    <tr>
      <td>Tron Nile Testnet</td>
      <td><code>tron:nile</code></td>
    </tr>

    <tr>
      <td>Tron Shasta Testnet</td>
      <td><code>tron:shasta</code></td>
    </tr>

    <tr>
      <td>Bitcoin (p2wpkh)</td>
      <td><code>bip122:000000000019d6689c085ae165831e93-p2wpkh</code></td>
    </tr>

    <tr>
      <td>Bitcoin Testnet (p2wpkh)</td>
      <td><code>bip122:000000000933ea01ad0ee984209779ba-p2wpkh</code></td>
    </tr>
  </tbody>
</table>

### Understanding the CAIP-2 Format

This includes the namespace (e.g. `eip155` for Ethereum-based chains) followed by the chain-specific identifier. It is designed to be chain-agnostic and supports a wider variety of blockchain networks beyond just EVM-compatible ones.

### Why CAIP-2?

The CAIP-2 format is essential for environments where multiple blockchain networks need to be identified and interacted with. It provides a standardized way to refer to chains, reducing ambiguity and enhancing interoperability across different platforms and applications.

***

Understanding both the traditional EVM chain ID format and the CAIP-2 format is crucial for interacting with multi-curve environments. If you have any questions or need further clarification, please reach out to our support team!