Bring Your Own Frontend

Build CoinFello into your own frontend by hitting the A2A endpoint directly. The API follows the Agent-to-Agent protocol spec.

Demo Project

A working example app showing authentication, streaming, and client-side tool call handling.

Endpoint

POST https://app.coinfello.com/api/a2a

All requests use JSON-RPC 2.0.

Methods

Method	Description
`message/send`	Send a message and get a response
`message/stream`	Send a message and stream the response via SSE
`tasks/get`	Get a task by ID (optionally limit history length)
`tasks/cancel`	Cancel a running task

Agent ID

Every message/send and message/stream request must include an agentId. The endpoint is agent-agnostic — the agent is resolved at request time from the value you supply. Pass it in params.configuration:

{
  "params": {
    "configuration": { "agentId": 1 },
    "message": { ... }
  }
}

Omitting agentId on a new request returns: "agentId is required: provide in configuration.agentId or as a DataPart". Once a task exists, subsequent messages that include its taskId do not need to repeat it. Find the numeric ID in the agent card under skills where each entry is a separate chat agent.

Example: Send a Message

curl -b cookies.txt -X POST https://app.coinfello.com/api/a2a \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "message/send",
    "params": {
      "configuration": { "agentId": 1 },
      "message": {
        "role": "user",
        "parts": [{ "type": "text", "text": "What are the best yields for ETH right now?" }]
      }
    }
  }'

Streaming

Use message/stream to get Server-Sent Events back. Each event is a JSON-RPC response wrapping an A2A stream event:

curl -b cookies.txt -X POST https://app.coinfello.com/api/a2a \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "message/stream",
    "params": {
      "configuration": { "agentId": 1 },
      "message": {
        "role": "user",
        "parts": [{ "type": "text", "text": "Swap 0.1 ETH to USDC" }]
      }
    }
  }'

Authentication

Authentication uses SIWE (Sign-In with Ethereum). Complete the SIWE flow to obtain a session cookie before making requests. See Authentication for the full flow with curl examples.

Client-side tool calls

The CoinFello chat agent which you can get from its agent card returns tool call requests as part of its A2A responses. Your frontend is responsible for handling these calls — rendering UI, prompting the user for approval, executing wallet transactions, and returning results back to the agent. Tool calls appear in the agent’s response as functionCall parts:

{
  "role": "agent",
  "parts": [
    {
      "type": "functionCall",
      "name": "execute_lifi_swap",
      "id": "call_abc123",
      "parameters": {
        "fromChainId": 1,
        "toChainId": 1,
        "fromTokenAddress": "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE",
        "toTokenAddress": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
        "fromAmount": "100000000000000000",
        "slippage": 0.005,
        "fromTokenSymbol": "ETH",
        "toTokenSymbol": "USDC",
        "fromTokenDecimals": 18,
        "toTokenDecimals": 6
      }
    }
  ]
}

After the user approves or the action completes, submit the result back via message/send with a functionReturn part:

{
  "role": "user",
  "parts": [
    {
      "type": "functionReturn",
      "id": "call_abc123",
      "name": "execute_lifi_swap",
      "result": { "txHash": "0xabc..." }
    }
  ]
}

Tool reference

call_smart_contract_function

Proposes a generic smart contract call for the user to approve or reject. Display the contract address, function name, arguments, and value before submitting the transaction.

Parameter	Type	Description
`to`	`string`	Contract address
`functionName`	`string`	Name of the contract function
`args`	`string[]`	Encoded function arguments
`chainId`	`number`	Target chain ID
`value`	`string`	Native token value in wei
`abi`	`string[]`	ABI fragments needed to encode the call

send_native_gas_token

Sends native gas token (e.g. ETH) to an address. Show the recipient and amount for user confirmation before broadcasting.

Parameter	Type	Description
`to`	`string`	Recipient address
`chainId`	`number`	Target chain ID
`value`	`string`	Amount in wei

transfer_nft

Transfers an NFT to another address. Display the NFT details and recipient before the user approves.

Parameter	Type	Description
`contractAddress`	`string`	NFT contract address
`tokenId`	`string`	Token ID
`toAddress`	`string`	Recipient address
`amount`	`string`	Amount (for ERC-1155; use `"1"` for ERC-721)
`chainId`	`number`	Target chain ID

show_token_balance_ui

Requests a visual token balance display. Render balance cards or a portfolio summary using the provided data — no wallet transaction required.

Parameter	Type	Description
`address`	`string`	Wallet address
`balances`	`object[]`	Array of token balance objects (symbol, amount, price, value, logo, etc.)
`totalValue`	`number`	Total portfolio value in USD

execute_lifi_swap

Executes a token swap or cross-chain bridge via LI.FI. Fetch a quote from LI.FI using the provided parameters, show the route to the user, then execute on approval.

Parameter	Type	Description
`fromChainId`	`number`	Source chain ID
`toChainId`	`number`	Destination chain ID
`fromTokenAddress`	`string`	Source token address
`toTokenAddress`	`string`	Destination token address
`fromAmount`	`string`	Amount in source token’s smallest unit
`slippage`	`number`	Slippage tolerance (e.g. `0.005` for 0.5%)
`fromTokenSymbol`	`string`	Source token symbol
`toTokenSymbol`	`string`	Destination token symbol
`fromTokenDecimals`	`number`	Source token decimals
`toTokenDecimals`	`number`	Destination token decimals

enter_staking_yield

Prepares a staking transaction for a specific yield opportunity. Show the APY, protocol, pool, and lockup period before requesting approval.

Parameter	Type	Description
`yieldId`	`string`	Yield opportunity ID
`amount`	`string`	Amount to stake
`walletAddress`	`string`	User’s wallet address
`tokenSymbol`	`string`	Token to stake
`tokenAddress`	`string`	Token contract address
`chainId`	`number`	Target chain ID
`network`	`string`	Network name
`protocol`	`string`	Protocol name
`poolName`	`string`	Pool name
`apy`	`number`	Current APY
`lockupPeriod`	`string`	Human-readable lockup duration
`rewardTokenSymbols`	`string[]`	Reward token symbols

exit_staking_yield

Prepares an unstaking transaction to withdraw from a staking position.

Parameter	Type	Description
`yieldId`	`string`	Yield opportunity ID
`amount`	`string`	Amount to withdraw
`walletAddress`	`string`	User’s wallet address

aave_supply / aave_borrow / aave_repay / aave_withdraw

Aave V4 lending market interactions. All four share the same parameter shape and require user approval before executing.

Parameter	Type	Description
`marketAddress`	`string`	Aave market contract address
`tokenAddress`	`string`	Token contract address
`tokenSymbol`	`string`	Token symbol
`amount`	`string`	Amount in token’s smallest unit
`walletAddress`	`string`	User’s wallet address
`chainId`	`number`	Target chain ID

request_auto_rebalance_permission

Asks the user to grant permission for automatic yield rebalancing. Display the current position, minimum yield increase threshold, and maximum lockup before the user accepts or declines.

Parameter	Type	Description
`chainId`	`number`	Target chain ID
`tokenAddress`	`string`	Token to rebalance
`currentPosition.protocol`	`string`	Current protocol
`currentPosition.amount`	`string`	Current staked amount
`currentPosition.apy`	`number`	Current APY
`minYieldIncrease`	`number`	Minimum APY improvement to trigger rebalance
`maxLockupDays`	`number`	Maximum lockup days the user will accept

React Package

Interested in a drop-in @coinfello/react package? Reach out to us — it’s on the roadmap.

Agent Integration

Walkthrough

Demo Project

Endpoint

Methods

Agent ID

Example: Send a Message

Streaming

Authentication

Client-side tool calls

Tool reference

React Package

Agent Integration

Walkthrough

Demo Project

​Endpoint

​Methods

​Agent ID

​Example: Send a Message

​Streaming

​Authentication

​Client-side tool calls

​Tool reference

​React Package

Endpoint

Methods

Agent ID

Example: Send a Message

Streaming

Authentication

Client-side tool calls

Tool reference

React Package