{"uid":"cap_cz4xmlQ5ED2VgRZHbQ5Sk","slug":"transaction-preflight-simulator-txpreflight-a239281d","name":"Transaction Preflight Simulator (txpreflight)","description":"Pay-per-call HTTP APIs, paid with x402 in USDC on Base (eip155:8453): agentkit, api-change-check, basedue, basewatch, chainread, check-sanctions, chgwatch, company-facts, composite, edgar, feednews, pageaudit, solcheck, token-dd, txpreflight, walletcheck, webmd, webread, websearch, x402index. Each operation describes its service.","url":"https://api.firstmention.uk/s/txpreflight/preflight?utm_source=zero.xyz","method":"POST","headers":{},"bodySchema":{"type":"object","properties":{"to":{"type":"string"},"data":{"type":"string"},"from":{"type":"string"},"owner":{"type":"string"},"token":{"type":"string"},"spender":{"type":"string"}}},"responseSchema":{"type":"json","example":{"ok":true,"chain":"base","ethUsd":2341.57,"chainId":8453,"summary":{"simulation":"call succeeds","baseFeeGwei":0.005,"gasEstimate":51542,"wouldRevert":false,"revertReason":null,"gasUnitsToSend":59274,"maxFeePerGasWei":"11000000","priorityFeeGwei":0.001,"expectedGasCostEth":3.56e-7,"expectedGasCostUsd":0.000833,"worstCaseGasCostUsd":0.001527,"effectiveGasPriceWei":"6000000","maxPriorityFeePerGasWei":"1000000"},"verdict":"safe-to-send","warnings":[],"asOfBlock":53042234,"latencyMs":337,"disclaimer":"Simulation against the latest block only. It is not a guarantee."}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.01","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.01/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.01","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.01","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_pfdjP8iI3NRkFz1qNl5gz","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.01","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Simulates an EVM transaction on Base mainnet before sending, returning gas estimates, revert checks, fee quotes, and a safe-to-send verdict.","exampleAgentPrompt":"Before I send my contract call to 0xAbC...123 on Base with this calldata 0xdeadbeef and value 0 wei, can you do a preflight simulation using normal fee urgency to check if it'll revert and what the gas cost will be in USD?","exampleUseCases":[{"title":"Safe DeFi swap pre-check","prompt":"I'm about to call a Uniswap router on Base — the target is 0x2626664c2603336E57B271c5C0b26F421741e481, calldata is 0x04e45aaf000000000000..., value is 0 wei, and my wallet is 0xMyWallet. Run a preflight with normal urgency and tell me if it'll revert and what I'll pay in gas."},{"title":"NFT mint gas estimation","prompt":"Can you simulate an NFT mint transaction before I send it? Target contract is 0xNFTContract on Base, calldata is 0xa0712d68 followed by the token count, no ETH value needed. Use fast urgency so I can see the worst-case gas cost in USD."},{"title":"Plain ETH transfer cost check","prompt":"I want to send some ETH to 0xRecipient on Base — no calldata, value is 1000000000000000000 wei (1 ETH). Run a slow-urgency preflight from my address 0xMySenderWallet and tell me the expected gas fee and whether it's safe to send."}],"resultDescription":"Returns a JSON object with ok status, chain info (Base, chainId 8453), current ETH/USD price, a detailed summary (gas estimate, base fee, max fee per gas, priority fee, expected and worst-case gas costs in ETH and USD), a human-readable simulation result, a verdict ('safe-to-send' or similar), any warnings, the block number used for simulation, latency, and a disclaimer that the simulation reflects the latest block only.","failureModes":["Invalid or malformed 0x address for 'to' field returns error","Malformed calldata hex causes parsing failure","Transaction simulation shows revert with revertReason populated and wouldRevert: true","Network or RPC node unavailability causes 5xx error","Stale block data if the Base node lags behind head","Payment not accepted (x402) if USDC balance insufficient"],"whenToPreferThis":"Use this endpoint when you need a real-time, pay-per-call preflight simulation of any EVM transaction on Base mainnet — particularly when you want gas estimates, revert prediction, fee tier quotes (slow/normal/fast), and a safe-to-send verdict in a single call. Prefer this over generic gas APIs when you need actual calldata simulation (not just transfer estimates) and USD-denominated cost breakdowns against a live ETH price. It is paid per-call in USDC via x402, making it suitable for agent workflows where cost-per-query matters.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-29T12:36:53.726Z","isFirstParty":false,"canonicalSlug":"transaction-preflight-simulator-txpreflight-a239281d"}