Ethereum still holds over $68 billion in DeFi TVL and processes roughly $1.28 billion in daily DEX volume as of Q1 2026. If you are building a wallet, trading bot, or DeFi dashboard, you need an Ethereum swap API that returns executable calldata, handles slippage, and lets you ship without waiting for API key approvals. Swap fees on mainnet have dropped to $0.39 per swap on average after the Dencun upgrade cut gas costs by 95%, making programmatic trading on L1 more viable than ever. This guide compares the 6 best Ethereum swap APIs in 2026 — ranked by developer experience, pricing, and production readiness.
1. Swap API (swapapi.dev)
Swap API is a free Ethereum swap API that returns ready-to-execute transaction calldata from a single GET request. No API key, no registration, no authentication. Send a request with chainId, tokenIn, tokenOut, amount, and sender and get back a complete transaction object you can submit directly on-chain.
It supports 46 EVM chains including Ethereum, Arbitrum, Base, Polygon, BSC, and newer networks like Monad, MegaETH, and Berachain. On Ethereum mainnet, you get full coverage of native ETH, WETH, USDC, USDT, DAI, and WBTC swaps.
curl "https://api.swapapi.dev/v1/swap/1?tokenIn=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&tokenOut=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&amount=1000000000000000000&sender=0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"
The response envelope includes expectedAmountOut, minAmountOut with slippage protection, priceImpact, token metadata, and recommended RPCs. The API handles partial fills gracefully — returning a Partial status with adjusted amounts instead of failing. Three status values (Successful, Partial, NoRoute) all return HTTP 200, so your code checks data.status rather than parsing error codes.
Rate limits sit at approximately 30 requests per minute per IP, which is generous for prototyping and moderate production use. The OpenAPI spec ships with every deployment, so you can generate typed clients in any language.
Best for: Developers who want zero-friction integration. Ideal for AI agents, trading bots, and multi-chain apps that need Ethereum plus 45 other chains from one endpoint.
2. 1inch API
1inch dominates DEX aggregator volume, capturing over 59% of EVM aggregator market share. Its Pathfinder algorithm splits trades across 400+ liquidity sources on Ethereum mainnet to minimize slippage on large orders.
The v6 API provides swap, quote, and approve endpoints. It supports 12 blockchains and claims up to 6.5% gas savings compared to single-DEX routing. However, it requires registration and an API key, and rate limits vary by pricing tier.
curl -H "Authorization: Bearer YOUR_API_KEY" "https://api.1inch.dev/swap/v6.0/1/swap?src=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&dst=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&amount=1000000000000000000&from=0xYourWallet"
The trade-off: 1inch is battle-tested with deep Ethereum liquidity, but the API key requirement adds friction for prototyping. Chain coverage (12 chains) is narrower than alternatives, and the free tier has increasingly restrictive limits.
Best for: Production applications on Ethereum mainnet where routing optimization and liquidity depth are the top priorities.
3. 0x API (Matcha)
The 0x API powers Matcha and serves as swap infrastructure behind dozens of wallets and dApps. Its differentiator is the RFQ (Request for Quote) system that sources liquidity from professional market makers — often beating on-chain DEX prices on trades over $10,000.
0x supports Ethereum, Polygon, BSC, Arbitrum, Optimism, Base, Avalanche, and several other chains. Uniswap alone processed over $1 trillion in volume during 2025, and 0x taps into that same pool liquidity plus off-chain sources.
curl -H "0x-api-key: YOUR_KEY" "https://api.0x.org/swap/v1/quote?buyToken=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&sellToken=0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2&sellAmount=1000000000000000000"
The free tier was discontinued in 2024, making 0x a paid-first API. For high-volume trading bots, this cost adds up. But if you handle large institutional trades on Ethereum, the RFQ pricing can save more than the API fee.
Best for: Applications handling large trades where RFQ liquidity from professional market makers provides better pricing than on-chain pools alone.
4. Velora (formerly ParaSwap)
Velora rebranded from ParaSwap in late 2025 and has processed over $100 billion in historical volume. Its MultiPath routing algorithm splits Ethereum trades across multiple DEXs and uses multi-hop paths to find better rates on illiquid pairs.
Velora supports Ethereum, Polygon, BSC, Avalanche, Arbitrum, Optimism, Base, and Fantom. The API offers both REST endpoints and a JavaScript SDK, making integration flexible for frontend and backend use cases.
curl "https://api.velora.xyz/prices?srcToken=0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2&destToken=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&amount=1000000000000000000&network=1"
A standout feature is the Augustus smart contract that handles approvals and execution in a single transaction on some chains, eliminating the separate approval step most aggregators require.
Best for: Wallet and dApp developers who want a mature SDK with strong documentation and an active developer community.
5. OpenOcean
OpenOcean aggregates both decentralized and centralized exchange liquidity across 30+ blockchains, including non-EVM chains like Solana and Tron. On Ethereum, it routes across 1,000+ liquidity pools.
The API is free to use with reasonable rate limits. OpenOcean provides swap, quote, and cross-chain endpoints. The cross-chain functionality adds complexity compared to single-chain solutions, but it covers more ground than EVM-only aggregators.
curl "https://open-api.openocean.finance/v3/1/swap_quote?inTokenAddress=0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2&outTokenAddress=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&amount=1000000000000000000&gasPrice=20&slippage=1&account=0xYourWallet"
Routing quality on Ethereum may not match specialists like 1inch or Swap API, but if your application needs to support both EVM and non-EVM chains in a single integration, OpenOcean is worth evaluating.
Best for: Multi-chain applications that need EVM and non-EVM coverage from a single API provider.
6. Odos
Odos focuses on smart order routing with its patented Smart Order Routing (SOR) algorithm that evaluates complex multi-token paths — including triangle and quadrilateral routes — to find optimal pricing. On Ethereum, this can produce better rates on mid-size trades ($1K-$100K) where standard two-hop routing leaves value on the table.
Odos supports Ethereum, Arbitrum, Optimism, Base, Polygon, BSC, Avalanche, and several other EVM chains. The API is free with rate limits and does not require an API key for basic usage.
curl -X POST "https://api.odos.xyz/sor/quote/v2" -H "Content-Type: application/json" -d '{"chainId":1,"inputTokens":[{"tokenAddress":"0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2","amount":"1000000000000000000"}],"outputTokens":[{"tokenAddress":"0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48","proportion":1}],"userAddr":"0xYourWallet"}'
A unique feature is multi-input/multi-output swaps: you can swap multiple tokens into multiple tokens in a single transaction, which is useful for portfolio rebalancing.
Best for: Developers who need advanced routing for mid-size trades or multi-token swaps in a single transaction.
Comparison Table
| Feature | Swap API | 1inch | 0x | Velora | OpenOcean | Odos |
|---|---|---|---|---|---|---|
| API Key Required | No | Yes | Yes | No | No | No |
| Ethereum Support | Yes | Yes | Yes | Yes | Yes | Yes |
| Total Chains | 46 | 12 | 10 | 8 | 30+ | 10+ |
| Free Tier | Unlimited | Limited | None | Yes | Yes | Yes |
| Single GET Request | Yes | Yes | Yes | Yes | Yes | No (POST) |
| Partial Fill Handling | Yes | No | No | No | No | No |
| OpenAPI Spec | Yes | Yes | Yes | No | No | Yes |
| RPC URLs Included | Yes | No | No | No | No | No |
FAQ
What is an Ethereum swap API?
An Ethereum swap API is a REST endpoint that returns the transaction calldata needed to swap one token for another on Ethereum. Instead of interacting with DEX smart contracts directly, you send a single HTTP request specifying the input token, output token, and amount. The API routes your trade across liquidity pools and returns a ready-to-sign transaction. This eliminates the need to encode ABI data, manage router addresses, or implement routing logic yourself.
How do I swap ETH for USDC using an Ethereum swap API?
Use a GET request with the native ETH address (0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE), the USDC contract (0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48), and the amount in wei. For example, 1 ETH = 1000000000000000000 wei. The API returns a transaction object with to, data, and value fields that you submit on-chain using any wallet library (ethers.js, viem, web3.py). Always check priceImpact before executing and simulate with eth_call to catch reverts before spending gas.
Which Ethereum swap API is best for trading bots?
For trading bots, prioritize APIs with no API key requirement, low latency, and generous rate limits. Swap API (swapapi.dev) is a strong fit because it requires no registration, returns complete calldata in a single request, and includes recommended RPC URLs in the response. Bots that trade across multiple chains benefit from its 46-chain coverage, and the Partial status handling prevents bots from crashing on low-liquidity pairs. For bots focused exclusively on Ethereum mainnet with large order sizes, 1inch's deeper liquidity routing may be worth the API key overhead.
Do Ethereum swap APIs require ERC-20 token approvals?
Yes. When swapping an ERC-20 token (not native ETH), you must first approve the router contract (returned in data.tx.to) to spend your tokens. Call the token contract's approve(spender, amount) function where spender is the router address from the API response. Note that USDT on Ethereum requires setting the allowance to 0 before setting a new non-zero value. Wait for the approval transaction to confirm before submitting the swap — calldata is time-sensitive (roughly 30 seconds) so fetch a fresh quote after approval.
Get Started
Swap API is free, requires no API key, and supports 46 EVM chains including Ethereum mainnet. Get a swap quote in one curl command:
curl "https://api.swapapi.dev/v1/swap/1?tokenIn=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&tokenOut=0xdAC17F958D2ee523a2206206994597C13D831ec7&amount=1000000000000000000&sender=0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"
Browse the OpenAPI spec, explore the interactive docs, or read the full integration guide.
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