How to Use the Harmonyscan (Harmony One Block Explorer API) MCP in LangChain

Q: How do I add the Harmonyscan (Harmony One Block Explorer API) tools to my LangChain agent?

You use the MultiServerMCPClient from the LangChain MCP adapter package. After you initialize the client with the server URL, call client.gettools() and pass the resulting list directly to your agent executor.

Q: Can my agent check if a Harmony transaction succeeded?

Yes. Give the agent the gettxreceiptstatus tool. It takes a transaction hash and returns a '1' for success or a '0' for failure. It's a simple way to confirm finality.

Q: How does this MCP server help with smart contract development in LangChain?

You can build an agent that uses getsourcecode and getabi to retrieve contract details. Your agent can then analyze the code or use the ABI to formulate calls to proxyrequest, helping you test contract interactions.

Build agents in LangChain that interact with the Harmony blockchain. Query balances, track transactions, and read contract data.

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Connect Harmonyscan (Harmony One Block Explorer API) MCP to LangChain

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Setup Harmonyscan (Harmony One Block Explorer API) with LangChain

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Perplexity

Chain On-Chain Data

Your LangChain agent can now pull Harmony transaction data directly. The tools are designed to be chained together for complex logic. For example, create a chain that first checks a wallet's balance with `get_balance`. If the balance is above a certain threshold, the next step in the chain calls `get_tx_list` to fetch and analyze its recent activity. The output of one tool becomes the input for the next.

Build Custom Harmony Tools with LangChain

Go beyond the pre-built tools using `proxy_request`. This tool gives your agent a direct line to the Harmony JSON-RPC endpoint. Now you can construct custom queries inside a LangChain tool definition. If you need a specific, niche piece of data not covered by the other 13 tools, you don't have to wait for an update. You just build the call yourself and let your agent run it.

Debug Agent Logic with Full Traces

Figure out exactly why your agent made a decision. When you connect this MCP server to LangChain, every tool call is automatically traced. You can see the exact inputs for a `get_abi` call and the full JSON output from Harmonyscan. This makes it much easier to debug complex chains that might be misinterpreting on-chain data from tools like `get_logs` or `get_token_tx`.

Setup guide

Set up Harmonyscan (Harmony One Block Explorer API) MCP in LangChain

Prerequisites

Python 3.10+ installed
langchain-mcp-adapters + langgraph packages
Active Vinkius subscription with a valid endpoint token

1

Install dependencies
Run pip install langchain-mcp-adapters langgraph langchain-openai. The MCP adapters package converts MCP tools into native LangChain BaseTool objects.
2

Connect via HTTP transport
Use MultiServerMCPClient with "transport": "http" pointing to your Vinkius endpoint. Replace [YOUR_TOKEN_HERE] with your token from cloud.vinkius.com.
3

Create a ReAct agent
Pass the discovered tools to create_react_agent() from LangGraph. The agent automatically routes Harmonyscan (Harmony One Block Explorer API) tool calls through the MCP protocol.
4

Run with any LLM
Swap ChatOpenAI for ChatAnthropic, ChatGoogleGenerativeAI, or any LangChain-compatible model. The MCP tools work identically across all providers.

agent.py

from langchain_mcp_adapters.client import MultiServerMCPClient
from langgraph.prebuilt import create_react_agent
from langchain_openai import ChatOpenAI

async with MultiServerMCPClient({
    "harmonyscan-harmony-one-block-explorer-api-mcp": {
        "transport": "http",
        "url": "https://edge.vinkius.com/[YOUR_TOKEN_HERE]/mcp",
    }
}) as client:
    tools = client.get_tools()

    agent = create_react_agent(
        ChatOpenAI(model="gpt-4o"),
        tools,
    )
    result = await agent.ainvoke({
        "messages": "List recent Harmonyscan (Harmony One Block Explorer API) transactions"
    })
    print(result["messages"][-1].content)

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Common questions about Harmonyscan (Harmony One Block Explorer API) MCP in LangChain

You use the `MultiServerMCPClient` from the LangChain MCP adapter package. After you initialize the client with the server URL, call `client.get_tools()` and pass the resulting list directly to your agent executor.

Yes. Give the agent the `get_tx_receipt_status` tool. It takes a transaction hash and returns a '1' for success or a '0' for failure. It's a simple way to confirm finality.

Start with LangGraph. It lets you define your agents and tools as nodes in a graph, giving you precise control over the flow of logic. For example, a node can call `get_balance_multi` and the graph can branch based on the results.

You can build an agent that uses `get_source_code` and `get_abi` to retrieve contract details. Your agent can then analyze the code or use the ABI to formulate calls to `proxy_request`, helping you test contract interactions.

The server itself is stateless and ephemeral; it doesn't store your data. Any data you request, like wallet balances from `get_balance` or transaction lists from `get_tx_list`, is passed through the server to your LangChain agent. Be aware that if you use tracing services, those inputs and outputs may be logged there.

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