{"uid":"cap_ADVxUAFUiavJJ0_DBzPG2","slug":"transaction-preflight-c950cd38","name":"Transaction Preflight","description":"Simulates an unsigned Base or Base Sepolia EVM transaction with read-only RPC calls before an agent signs or broadcasts it. Returns execution/revert status, gas estimate, decoded top-level ERC-20 transfers and approvals, unlimited-approval warnings, and a risk signal. It never signs, holds keys, or broadcasts. Standard RPC does not expose complete internal/token state diffs.","url":"https://mcp.dropenginehq.com/api/simulate-transaction?utm_source=zero.xyz","method":"POST","headers":{},"bodySchema":{"type":"object","properties":{"to":{"type":"string","pattern":"^0x[a-fA-F0-9]{40}$"},"data":{"type":"string","pattern":"^0x(?:[a-fA-F0-9]{2})*$","maxLength":131074},"from":{"type":"string","pattern":"^0x[a-fA-F0-9]{40}$"},"chain":{"enum":["base","base-sepolia"],"type":"string"},"value":{"type":"string","pattern":"^(?:0|[1-9]\\d*)$","maxLength":78}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.02","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":"$0.02/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_xh4QCJUJDJe4aN1nRG60D","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.02","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Simulates an unsigned EVM transaction on Base or Base Sepolia before signing, returning gas estimates, revert status, ERC-20 token transfer/approval decoding, and risk signals.","exampleAgentPrompt":"Before I sign this transaction, simulate it on Base mainnet — the contract is 0xAbC...123, my wallet is 0xDef...456, and the calldata is 0xa9059cbb000...0064. Tell me if it will revert, how much gas it needs, any ERC-20 transfers or approvals it triggers, and flag it if there's an unlimited approval.","exampleUseCases":[{"title":"DeFi swap safety check","prompt":"Before I approve this DEX swap transaction on Base, simulate it for me — from my wallet 0x1234...abcd to the router at 0x5678...ef01, calldata 0x38ed1739...0001, value 0. Tell me if it will succeed, how much gas it'll use, and whether it's trying to grab an unlimited token approval."},{"title":"Unlimited approval detection","prompt":"I'm about to sign an ERC-20 approve call on Base — from 0xAAAA...1111 to the spender at 0xBBBB...2222, calldata 0x095ea7b3...ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff. Simulate it and warn me if it's granting unlimited approval before I sign."},{"title":"Pre-broadcast revert check on testnet","prompt":"Simulate this contract interaction on Base Sepolia for me before I broadcast it — from 0xDEAD...BEEF to 0xC0FF...EE00, with calldata 0x1234abcd and no ETH value. I just want to know if it will revert and what the gas estimate is."}],"resultDescription":"Returns whether the transaction would succeed or revert, a gas usage estimate, decoded top-level ERC-20 transfer and approval events (with amounts and token addresses), warnings for unlimited approvals, and a risk signal — without ever broadcasting, signing, or holding keys.","failureModes":["Invalid hex calldata format returns a 400-level error","Unknown or unsupported chain value (not 'base' or 'base-sepolia') causes rejection","Simulation may not capture internal/nested call state diffs that standard RPC doesn't expose","Very large calldata (near 131074 char limit) may cause timeouts","Contract not deployed at target address on the specified chain causes revert result"],"whenToPreferThis":"Use this endpoint when an AI agent needs to verify an EVM transaction's safety before signing or broadcasting on Base or Base Sepolia — especially for detecting reverts, estimating gas, or identifying unlimited ERC-20 approvals. Prefer this over raw RPC simulation when you want structured, decoded token transfer and approval output plus a risk signal without implementing custom ABI decoding.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-02T00:44:26.456Z","isFirstParty":false,"canonicalSlug":"transaction-preflight-c950cd38"}