Getting Started

swapapi is a free token swap API that returns executable calldata. No API key, no account, no SDK — just a GET request and you get back a transaction ready to submit on-chain.

Base URL: https://api.swapapi.dev

---

Your first request

Swap 1 ETH for USDC on Ethereum mainnet:

curl "https://api.swapapi.dev/v1/swap/1?\
tokenIn=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&\
tokenOut=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&\
amount=1000000000000000000&\
sender=0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"

That's it. There is no step 2.

---

The response

{
  "success": true,
  "data": {
    "status": "Successful",
    "tokenFrom": {
      "address": "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE",
      "symbol": "ETH",
      "name": "Ether",
      "decimals": 18
    },
    "tokenTo": {
      "address": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
      "symbol": "USDC",
      "name": "USD Coin",
      "decimals": 6
    },
    "swapPrice": 2435.12,
    "priceImpact": 0.0003,
    "amountIn": "1000000000000000000",
    "expectedAmountOut": "2435120000",
    "tx": {
      "from": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
      "to": "0x011E52E4E40CF9498c79e329EBc29ed08c8B5abB",
      "data": "0x2646478b...",
      "value": "1000000000000000000",
      "gasPrice": 30000000000,
      "gas": "250000"
    }
  },
  "timestamp": "2026-03-12T00:00:00.000Z"
}

Field reference

Field	Type	Description
success	boolean	true if the request succeeded
data.status	string	"Successful", "Partial", or "NoRoute"
data.tokenFrom	object	Input token metadata (address, symbol, name, decimals)
data.tokenTo	object	Output token metadata (address, symbol, name, decimals)
data.swapPrice	number	Exchange rate (output per input token)
data.priceImpact	number	Price impact as a decimal (0.001 = 0.1%)
data.amountIn	string	Input amount in wei (same as your request)
data.expectedAmountOut	string	Guaranteed minimum output amount in token's smallest unit
data.tx.from	string	Your sender address
data.tx.to	string	Router contract address
data.tx.data	string	Encoded calldata — submit this on-chain
data.tx.value	string	Native token value to send (non-zero for native ETH swaps)
data.tx.gasPrice	number	Suggested gas price in wei
data.tx.gas	string	Estimated gas limit
timestamp	string	ISO 8601 response timestamp

---

Submit the swap (curl + JSON-RPC)

You can go from quote to on-chain execution with nothing but curl. No libraries, no SDKs.

1. Get the quote

curl -s "https://api.swapapi.dev/v1/swap/8453?\
tokenIn=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&\
tokenOut=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913&\
amount=1000000000000000000&\
sender=0xYOUR_ADDRESS" | jq .

2. Sign the transaction locally

You need to sign the tx object from the response. Use cast (from Foundry):

# Using the tx fields from the response:
cast send \
  --rpc-url https://mainnet.base.org \
  --private-key 0xYOUR_PRIVATE_KEY \
  0x011E52E4E40CF9498c79e329EBc29ed08c8B5abB \
  --value 1000000000000000000 \
  --gas-limit 250000 \
  --data 0x2646478b...

3. Or use raw JSON-RPC

If you don't have cast, you can sign with any tool and broadcast the raw signed transaction via RPC:

# eth_sendRawTransaction — broadcast a signed transaction
curl -X POST https://mainnet.base.org \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_sendRawTransaction",
    "params": ["0xSIGNED_TX_HEX"],
    "id": 1
  }'

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0xtransaction_hash..."
}

4. Check the result

# eth_getTransactionReceipt — check if it confirmed
curl -X POST https://mainnet.base.org \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_getTransactionReceipt",
    "params": ["0xYOUR_TX_HASH"],
    "id": 1
  }'

The signing step

The API gives you unsigned transaction data. You must sign it with the sender's private key before broadcasting. This is the one step that requires a tool — cast, a wallet library, or any ECDSA signer. The API never touches your private key.

Full script (bash + cast)

A complete swap in one script, zero dependencies beyond curl and cast:

#!/bin/bash
set -e

RPC_URL="https://mainnet.base.org"
SENDER="0xYOUR_ADDRESS"
PRIVATE_KEY="0xYOUR_PRIVATE_KEY"

# 1. Get swap quote
RESPONSE=$(curl -s "https://api.swapapi.dev/v1/swap/8453?\
tokenIn=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&\
tokenOut=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913&\
amount=1000000000000000000&\
sender=$SENDER")

# 2. Parse the tx fields
TX_TO=$(echo "$RESPONSE" | jq -r '.data.tx.to')
TX_DATA=$(echo "$RESPONSE" | jq -r '.data.tx.data')
TX_VALUE=$(echo "$RESPONSE" | jq -r '.data.tx.value')
TX_GAS=$(echo "$RESPONSE" | jq -r '.data.tx.gas')
EXPECTED_OUT=$(echo "$RESPONSE" | jq -r '.data.expectedAmountOut')

echo "Swapping 1 ETH for minimum $(echo "scale=2; $EXPECTED_OUT / 1000000" | bc) USDC"

# 3. Sign and send
cast send \
  --rpc-url "$RPC_URL" \
  --private-key "$PRIVATE_KEY" \
  "$TX_TO" \
  --value "$TX_VALUE" \
  --gas-limit "$TX_GAS" \
  --data "$TX_DATA"

---

Quick reference

Endpoint: GET https://api.swapapi.dev/v1/swap/{chainId}
Auth: None
Rate limit: 60 requests/minute per IP
Chains: Ethereum (1), Base (8453), Arbitrum (42161), Polygon (137), Optimism (10), and more
OpenAPI spec: api.swapapi.dev/openapi.json