getLatestPrice

Instructions

Implementation Reference

• index.js:41-90 (handler)

  The async handler function that fetches the latest Chainlink price for a given pair on a specified chain using ethers.js, including validation, provider setup, contract call to latestRoundData, and formatted response.

  async ({ pair, chain }) => {
    try {
      // Validate inputs
      const chainKey = chain.toLowerCase();
      latestPriceSchema.parse({ pair, chain });
  
      // Find feed by pair
      const feed = feedsData[chainKey].feeds.find((f) => f.name.toLowerCase() === pair.toLowerCase());
      if (!feed) {
        throw new Error(`Pair ${pair} not found on chain ${chain}`);
      }
  
      // Initialize provider and contract
      const provider = new ethers.JsonRpcProvider(`${feedsData[chainKey].baseUrl}/${process.env.INFURA_API_KEY}`);
      const priceFeedContract = new ethers.Contract(feed.proxyAddress, priceFeedAbi, provider);
  
      // Fetch decimals and latest round data
      const [decimals, roundData] = await Promise.all([
        priceFeedContract.decimals(),
        priceFeedContract.latestRoundData()
      ]);
  
      const price = ethers.formatUnits(roundData.answer, decimals);
      const timestamp = Number(roundData.updatedAt) * 1000;
  
      return {
        content: [{
          type: 'text',
          text: JSON.stringify({
            chain,
            pair,
            price: Number(price),
            decimals: Number(decimals),
            roundId: roundData.roundId.toString(),
            timestamp: new Date(timestamp).toISOString(),
            proxyAddress: feed.proxyAddress,
            feedCategory: feed.feedCategory
          }, null, 2)
        }]
      };
    } catch (error) {
      return {
        content: [{
          type: 'text',
          text: `Error: ${error.message}`
        }],
        isError: true
      };
    }
  }

• index.js:29-34 (schema)

  Zod input schema defining 'pair' and 'chain' parameters with validation for supported chains.

  const latestPriceSchema = z.object({
    pair: z.string().describe('The price feed pair, e.g., FIL/ETH or FDUSD/USD'),
    chain: z.string().refine((val) => feedsData[val.toLowerCase()], {
      message: 'Unsupported chain'
    }).describe('The blockchain network, e.g., ethereum or base')
  });

• index.js:37-91 (registration)

  MCP server.tool registration call for 'getLatestPrice' tool, including name, description, schema reference, and inline handler.

  server.tool(
    'getLatestPrice',
    'Fetches the latest price for a given pair on a specified chain',
    latestPriceSchema,
    async ({ pair, chain }) => {
      try {
        // Validate inputs
        const chainKey = chain.toLowerCase();
        latestPriceSchema.parse({ pair, chain });
  
        // Find feed by pair
        const feed = feedsData[chainKey].feeds.find((f) => f.name.toLowerCase() === pair.toLowerCase());
        if (!feed) {
          throw new Error(`Pair ${pair} not found on chain ${chain}`);
        }
  
        // Initialize provider and contract
        const provider = new ethers.JsonRpcProvider(`${feedsData[chainKey].baseUrl}/${process.env.INFURA_API_KEY}`);
        const priceFeedContract = new ethers.Contract(feed.proxyAddress, priceFeedAbi, provider);
  
        // Fetch decimals and latest round data
        const [decimals, roundData] = await Promise.all([
          priceFeedContract.decimals(),
          priceFeedContract.latestRoundData()
        ]);
  
        const price = ethers.formatUnits(roundData.answer, decimals);
        const timestamp = Number(roundData.updatedAt) * 1000;
  
        return {
          content: [{
            type: 'text',
            text: JSON.stringify({
              chain,
              pair,
              price: Number(price),
              decimals: Number(decimals),
              roundId: roundData.roundId.toString(),
              timestamp: new Date(timestamp).toISOString(),
              proxyAddress: feed.proxyAddress,
              feedCategory: feed.feedCategory
            }, null, 2)
          }]
        };
      } catch (error) {
        return {
          content: [{
            type: 'text',
            text: `Error: ${error.message}`
          }],
          isError: true
        };
      }
    }
  );