web3-mcp-server

Instructions

Implementation Reference

• src/tools/FetchTokenBalance.ts:13-34 (handler)

  The main asynchronous handler function that fetches the ERC20 token balance for a given wallet on a specific chain using viem library.

  export const fetchTokenBalance = async (options: FetchTokenBalanceOptions) => {
    const { tokenAddress, chainId, walletAddress } = options;
  
    const chain = getChainById(chainId);
    const client = createClient(chain);
  
    const contract = getContract({
      address: tokenAddress as `0x${string}`,
      abi: erc20Abi,
      client,
    });
  
    const [balance, decimals] = await Promise.all([
      contract.read.balanceOf([walletAddress as `0x${string}`]),
      contract.read.decimals(),
    ]);
  
    return {
      balance: balance.toString(),
      formattedBalance: formatUnits(balance, decimals),
    };
  };

• src/tools/FetchTokenBalance.ts:6-10 (schema)

  Zod schema defining the input parameters: tokenAddress, chainId, and walletAddress with validation.

  export const FetchTokenBalanceSchema = z.object({
    tokenAddress: z.string().startsWith("0x"),
    chainId: z.number(),
    walletAddress: z.string().startsWith("0x"),
  });

• src/index.ts:46-49 (registration)

  Registration of the tool in the ListToolsRequestSchema handler, specifying name, description, and input schema.

    name: "fetch_token_balance",
    description: "Get the balance of a token",
    inputSchema: z.toJSONSchema(FetchTokenBalanceSchema),
  },

• src/index.ts:122-140 (registration)

  Dispatch handler in the CallToolRequestSchema switch statement that parses arguments, calls fetchTokenBalance, and formats the response.

  case "fetch_token_balance": {
    const args = FetchTokenBalanceSchema.parse(request.params.arguments);
    const result = await fetchTokenBalance(args);
  
    return {
      content: [
        {
          type: "text",
          text: result.balance,
          description: "The balance of the token",
        },
        {
          type: "text",
          text: result.formattedBalance,
          description: "The formatted balance of the token",
        },
      ],
    };
  }