Build

POST /v1/build takes a quote_id from a previous Quote response and assembles an unsigned transaction ready for wallet signing and on-chain submission. This is the second step in the swap flow.

New to the API? Start with Getting Started for authentication and your first quote request.

Basic Build

Assemble a transaction from a quote:

curl -X POST "https://api.infraredtrading.com/v1/build" \
  -H "Content-Type: application/json" \
  -H "X-API-Key: YOUR_API_KEY" \
  -d '{
    "quote_id": "550e8400-e29b-41d4-a716-446655440000"
  }'

Build with Permit2 Signature

Attach a Permit2 signature for gasless token approval. The signature comes from signing the permit2.eip712 typed data returned in the quote response (when requested with include_permit2=true):

curl -X POST "https://api.infraredtrading.com/v1/build" \
  -H "Content-Type: application/json" \
  -H "X-API-Key: YOUR_API_KEY" \
  -d '{
    "quote_id": "550e8400-e29b-41d4-a716-446655440000",
    "permit2_signature": "0x1234567890abcdef..."
  }'

The permit2_signature is silently ignored if the original quote was not requested with include_permit2=true.

Build with Simulation

Run a fork simulation on the assembled transaction before returning. The simulation verifies the transaction will succeed and reports actual output amounts:

curl -X POST "https://api.infraredtrading.com/v1/build" \
  -H "Content-Type: application/json" \
  -H "X-API-Key: YOUR_API_KEY" \
  -d '{
    "quote_id": "550e8400-e29b-41d4-a716-446655440000",
    "simulate": true
  }'

Simulation failures do not block the response -- the transaction is still returned with simulation.success=false and an error message.

Request Fields

Field	Type	Required	Default	Description
quote_id	string	Yes	--	Quote identifier from a previous /v1/quote response.
permit2_signature	string	No	--	Hex-encoded Permit2 signature from signing the EIP-712 typed data in the quote's permit2 field.
simulate	boolean	No	false	Run fork simulation on the assembled transaction.

Quotes can be built multiple times -- building does not consume or invalidate the quote.

Response Fields

A successful response returns HTTP 200:

{
  "data": {
    "transaction": {
      "to": "0x1111111111111111111111111111111111111111",
      "data": "0x5ca02d52000000000000000000000000...",
      "value": "0",
      "gas": 250000,
      "chain_id": 1
    },
    "estimated_outputs": [
      {
        "token": "0x6B175474E89094C44Da98b954EedeBC836211103",
        "chain_id": 1,
        "expected_amount": "1850000000000000000000",
        "minimum_amount": "1831500000000000000000"
      }
    ]
  }
}

transaction

Unsigned transaction ready for wallet signing:

Field	Type	Description
to	string	ExecutionProxy contract address (EIP-55 checksummed).
data	string	ABI-encoded calldata for the ExecutionProxy.
value	string	ETH value to send in wei (decimal string). "0" for ERC-20 only swaps.
gas	integer	Recommended gas limit for the transaction.
chain_id	integer	Target blockchain network ID.

estimated_outputs

Carried forward from the quote. Same structure as the Quote response.

simulation

Only present when simulate=true. Fork simulation result:

Field	Type	Description
success	boolean	Whether the simulation succeeded.
gas_used	integer	Actual gas consumed in simulation. Only present on success.
output_amounts	object	Map of token addresses to simulated output amounts. Only present on success.
error	string	Error message if simulation failed (e.g., "execution reverted: INSUFFICIENT_OUTPUT_AMOUNT").

Example with simulation:

{
  "data": {
    "transaction": { ... },
    "estimated_outputs": [ ... ],
    "simulation": {
      "success": true,
      "gas_used": 185000,
      "output_amounts": {
        "0x6B175474E89094C44Da98b954EedeBC836211103": "1848500000000000000000"
      }
    }
  }
}

What to Do Next

After receiving the build response:

1. Check estimated outputs -- Verify the expected_amount and minimum_amount meet your requirements.

2. Review simulation results (if requested) -- If simulation.success is false, the transaction is likely to revert on-chain. Check the error field for details.

3. Sign the transaction -- Use the to, data, value, gas, and chain_id fields to construct and sign the transaction with the taker's wallet.

4. Submit on-chain -- Broadcast the signed transaction to the network. The transaction executes atomically through the ExecutionProxy contract -- all swaps succeed or the entire transaction reverts.

5. Handle ERC-20 approvals -- If the quote response included approvals, ensure the taker has approved the specified tokens and amounts for the spender address before submitting the transaction. Alternatively, use Permit2 to handle approvals via signature.