@sei-js SDK

TypeScript packages for building EVM applications on Sei

@sei-js is a set of TypeScript packages for building EVM applications on Sei. Use the packages for Sei-specific functionality, and use standard EVM libraries such as Viem or Ethers.js for everything else.

Sei is EVM-compatible, so you can also use Foundry, Hardhat, Wagmi, and other Ethereum tooling. @sei-js adds precompile ABIs, chain definitions, wallet integration, network metadata, scaffolding, and an MCP server.

@sei-js is open source. Contribute at github.com/sei-protocol/sei-js.

Current npm majors are ESM-only: @sei-js/precompiles@3, @sei-js/registry@2, @sei-js/create-sei@2, @sei-js/sei-global-wallet@2, and @sei-js/mcp-server@1. Use import. require() does not resolve these packages. @sei-js/precompiles needs Viem 2.55.16 or newer. The MCP server needs Node.js 20 or newer. @sei-js/ledger is not part of the current monorepo.

Why @sei-js?

• Typed ABIs and addresses for Sei precompiles
• Viem’s Pacific-1 and Atlantic-2 chain definitions re-exported for convenience, plus a seiLocal definition for local nodes
• Packages that work with standard EVM libraries

Packages

@sei-js/precompiles

Import precompile addresses and raw *_PRECOMPILE_ABI constants from the package root, @sei-js/precompiles/precompiles, or @sei-js/precompiles/viem. Ethers factories live on @sei-js/precompiles/ethers.

Viem owns the sei and seiTestnet chain definitions, so import those from viem/chains. The root and viem entrypoints re-export them if you would rather use a single import, and they also export seiLocal for a local node.

npm install @sei-js/precompiles@^3

@sei-js/create-sei

Create a Next.js dApp with wallet integration, TypeScript, and Sei network configuration.

npx @sei-js/create-sei app

@sei-js/sei-global-wallet

Add the EIP-6963 compatible Sei Global Wallet to a dApp.

npm install @sei-js/sei-global-wallet

@sei-js/registry

Use typed chain IDs, RPC endpoints, token metadata, and wallet information for Pacific-1 and Atlantic-2.

npm install @sei-js/registry

@sei-js/mcp-server

Connect an MCP-compatible AI assistant to Sei for blockchain queries, contract interactions, and documentation search.

npx @sei-js/mcp-server

Deprecated packages

The five packages above are the entire current monorepo. Every other @sei-js package is deprecated on npm and no longer maintained. If one of these appears in your package.json, migrate off it.

Deprecated package	What to use instead
@sei-js/evm	@sei-js/precompiles — same library, renamed
@sei-js/ledger	No replacement. See Ledger with ethers for the EVM signing flow
@sei-js/x402	@x402/core and @x402/evm. See x402 on Sei
@sei-js/x402-fetch	@x402/fetch and @x402/evm
@sei-js/x402-axios	@x402/axios and @x402/evm
@sei-js/x402-express	@x402/express, @x402/core, and @x402/evm
@sei-js/x402-hono	@x402/hono, @x402/core, and @x402/evm
@sei-js/x402-next	@x402/next, @x402/core, and @x402/evm
@sei-js/core	No replacement. Use Viem or Ethers.js for EVM access
@sei-js/cosmjs	No replacement
@sei-js/cosmos	No replacement
@sei-js/proto	No replacement

The last four covered Cosmos SDK access, which is deprecated under SIP-3. Build on the EVM instead.

Quick start

Generate a new Sei dApp:

npx @sei-js/create-sei app -n my-sei-app
cd my-sei-app
bun install
bun run dev

See Scaffold Sei for the generated template and CLI options.

Examples

End-to-end code examples using viem and ethers with Sei:

viem Quickstart

Read chain data, send transactions, and interact with contracts in a Node.js script or backend.

ethers v6 Quickstart

The same patterns using ethers v6, including browser provider and event listening.

Wagmi + React

Connect wallets, read balances, and write contracts in a React app using Wagmi hooks.

ERC-20 Interaction

Read metadata, check balances, transfer tokens, approve spenders, and query transfer history.

ERC-721 Interaction

Check ownership, transfer NFTs, manage approvals, and watch transfer events.

ERC-1155 Interaction

Batch balance queries, single and batch transfers, operator approvals, and event watching.

Multicall

Batch multiple contract reads into a single RPC call with Multicall3 and viem/ethers/wagmi.

Pointer Contracts

Look up pointer addresses for existing CW20 and CW721 contracts, then interact with them through ERC interfaces.

Sei Precompiles

Native balances, staking, rewards, and governance voting from JavaScript.

Deploy and Verify

Deploy contracts with viem, ethers, Foundry, or Hardhat and verify on Seiscan via Sourcify.

Transaction Lifecycle

Send transactions, wait for receipts, and decode event logs.

Error Handling

Decode reverts, handle wallet rejections, and retry transient RPC failures.

Community and support

• Discord: Join the Sei developer community
• GitHub Issues: Report bugs and request features