mcp-server

@sei-js/mcp-server

Enable AI assistants to interact with the Sei blockchain

Setup • GitHub • NPM • Telegram

Requirements

Node.js 20 or newer.

Quick Start

Basic Setup (Read-Only)

Start with read-only blockchain data access:

{
  "mcpServers": {
    "sei": {
      "command": "npx",
      "args": ["-y", "@sei-js/mcp-server"]
    }
  }
}

Wallet functionality is disabled by default.

Full Setup (With Wallet)

To enable transactions and wallet tools, set WALLET_MODE to private-key and provide a private key:

{
  "mcpServers": {
    "sei": {
      "command": "npx",
      "args": ["-y", "@sei-js/mcp-server"],
      "env": {
        "WALLET_MODE": "private-key",
        "PRIVATE_KEY": "0x123..."
      }
    }
  }
}

PRIVATE_KEY must be a valid 32-byte secp256k1 private key; the 0x prefix is optional. Startup fails instead of silently disabling wallet tools when private-key mode is misconfigured. Use a dedicated wallet with limited funds and never commit its private key.

Wallet mode is supported only with the default stdio transport. HTTP transports reject WALLET_MODE=private-key because exposing signing tools over HTTP would allow unsafe cross-origin requests.

Wallet-disabled mode still includes every non-signing tool, including contract reads, contract detection, gas estimates, token/NFT metadata, balances, and ownership checks. Only signing or broadcasting operations are hidden.

HTTP Transports

Transport selection is configured with SERVER_TRANSPORT; transport flags such as --http, --streamable-http, and --http-sse are not supported.

From a repository checkout, build the package and use the provided scripts:

bun run --cwd packages/mcp-server build
bun run --cwd packages/mcp-server start:http       # Streamable HTTP
bun run --cwd packages/mcp-server start:http-sse   # Legacy HTTP/SSE

To run the published package directly:

# Recommended: Streamable HTTP at http://localhost:8080/mcp
SERVER_TRANSPORT=streamable-http npx -y @sei-js/mcp-server

# Legacy HTTP/SSE: GET http://localhost:8080/mcp for the event stream,
# POST http://localhost:8080/mcp/message?sessionId=<id> for client messages
SERVER_TRANSPORT=http-sse npx -y @sei-js/mcp-server

Customize the listener with environment variables:

SERVER_TRANSPORT=streamable-http \
SERVER_HOST=127.0.0.1 \
SERVER_PORT=3001 \
SERVER_PATH=/api/mcp \
npx -y @sei-js/mcp-server

HTTP transports do not authenticate callers or validate Origin/Host. Bind to 127.0.0.1 for local use, and put any public exposure behind an authenticating reverse proxy.

http-sse is retained for older clients; use streamable-http for new integrations.

Each legacy SSE connection has an isolated MCP server session. Both HTTP transports close active MCP request/session resources during graceful shutdown, and listener startup failures (including an occupied port) terminate startup with a nonzero exit status.

Legacy SSE accepts at most 100 concurrent sessions by default. Set SSE_MAX_SESSIONS to a positive integer to tune the limit; excess connections receive HTTP 503. This limit reduces unauthenticated memory exhaustion risk but does not replace an authenticating reverse proxy.

Streamable HTTP accepts at most 100 active requests by default. Set STREAMABLE_HTTP_MAX_REQUESTS to a positive integer to tune the limit; excess requests receive HTTP 503.

HTTP transports create and close an isolated MCP server for each session or request; startup does not allocate an unused bootstrap server. Programmatic callers can use main(), which reports and rethrows ordinary startup failures. The packaged executable uses runCli() to convert those failures into exit code 1. The wallet-on-HTTP guard is stricter: it terminates immediately with exit code 1 before any listener or signing surface is created. Each main() call snapshots wallet configuration for that runtime, so a later start cannot expose signing tools on an already-running HTTP listener or rebind a still-running stdio server's signer.

Configuration

• SERVER_TRANSPORT: stdio (default), streamable-http, or http-sse
• SERVER_HOST: Nonempty HTTP listener host (default: localhost)
• SERVER_PORT: HTTP listener port (default: 8080)
• SERVER_PATH: HTTP endpoint path (default: /mcp). For http-sse, this is the GET event stream; clients POST messages to {SERVER_PATH}/message?sessionId=<id>.
• SSE_MAX_SESSIONS: Maximum concurrent legacy SSE sessions (default: 100)
• STREAMABLE_HTTP_MAX_REQUESTS: Maximum concurrent Streamable HTTP requests (default: 100)
• WALLET_MODE: disabled (default) or private-key
• PRIVATE_KEY: Private key used when WALLET_MODE=private-key
• MAINNET_RPC_URL: Optional custom Sei mainnet RPC URL
• TESTNET_RPC_URL: Optional custom Sei testnet RPC URL

Network arguments accept only the supported canonical names and chain ID strings:

• Sei mainnet: sei, 1329, or 0x531
• Sei testnet: sei-testnet, 1328, or 0x530

Unknown selectors are rejected and never fall back to mainnet. Configured RPC URLs are used only for upstream connections; MCP chain-info responses omit them, and upstream errors redact URLs and credential-bearing details.

Run npx -y @sei-js/mcp-server --help for the current configuration reference.