# Avasis Base Transaction Pre-Check > Avasis Base Transaction Pre-Check is a paid API for AI agents from agents.avasis.ai, paid per call via x402, $0.02/call, status unknown (last checked 2026-11-01). Simulates an Ethereum Base chain transaction before signing, returning revert risk, gas cost in USD, token transfers with USD values, approval risks, counterparty risk scores, and a SIGN/CAUTION/BLOCK verdict. ## Facts - Endpoint: GET https://agents.avasis.ai/v1/base/tx-precheck?utm_source=zero.xyz - Price: $0.02/call - Payment: x402 - Status: unknown - Last checked: 2026-11-01 - Activations on Zero: 0 - Tags: x402 - Canonical page: https://www.zero.xyz/c/avasis-base-transaction-pre-check-208f09a4 - Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_VsLrn6FGdywFj1i3kK5F9 Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently. ## How to call it through Zero Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`): ```sh zero fetch --capability avasis-base-transaction-pre-check-208f09a4 ``` Example prompt: Before I sign this transaction, can you simulate it on Base and tell me whether it'll revert, how much gas it'll cost in USD, what tokens will move, and whether I should sign it or block it? From wallet 0xYourWallet, to 0xContractAddress, with calldata 0xabcdef and 0 ETH value. ## When to prefer this Use this endpoint when an AI agent or wallet interface needs to validate a Base chain (chain 8453) transaction before the user signs it — especially when you need USD-denominated cost/transfer previews, approval risk scoring, GoPlus+OFAC counterparty checks, and a single SIGN/CAUTION/BLOCK verdict in one call. Prefer it over raw eth_simulateV1 calls when you want pre-parsed, human-readable risk output rather than raw simulation data. It is specifically scoped to Base; use sibling endpoints for Ethereum mainnet or Solana. ## Known failure modes - 502 Bad Gateway if the Base RPC node is down — no charge is applied - Missing required 'from' or 'to' query parameters returns a 400 validation error - Invalid hex format for 'data' or 'from'/'to' addresses returns a schema validation error - Calldata exceeding 6 KB is rejected - Simulation may return would_revert:true with a revert reason if the transaction would fail on-chain - If GoPlus or OFAC services are unavailable, counterparty risk fields may be null or incomplete ## How this service works Pre-sign tx precheck for Base (chain 8453, $0.02): simulate transaction {from,to,data,value} with eth_simulateV1 before signing. Returns would_revert + reason, gas USD, each ETH/ERC-20/NFT transfer with USD, wallet PnL (net_for_from usd_net), approval risk (spender, unlimited:true, USD exposure), counterparty risk (GoPlus + OFAC), decoded method, SIGN/CAUTION/BLOCK verdict with reasons. POST JSON or GET. Free live sample /v1/evm/tx-precheck/sample. Advice only; RPC down 502, never charged. ## Output A JSON object containing: chain identifier, simulation result (would_revert, revert reason), decoded method name and parameters, list of ETH/ERC-20/NFT transfers each with USD value, wallet net PnL (net_for_from with usd_net), array of approval risks (spender address, unlimited flag, USD exposure), counterparty risk scores from GoPlus and OFAC check, estimated gas cost in USD, and a final verdict object with SIGN / CAUTION / BLOCK decision plus human-readable reasons. ## Request schema (JSON Schema) ```json { "type": "object", "$schema": "https://json-schema.org/draft/2020-12/schema", "required": [ "input" ], "properties": { "input": { "type": "object", "required": [ "type", "method" ], "properties": { "type": { "type": "string", "const": "http" }, "method": { "enum": [ "GET" ], "type": "string" }, "queryParams": { "type": "object", "required": [ "from", "to" ], "properties": { "to": { "type": "string", "description": "the transaction's to (contract or recipient, 0x + 40 hex)" }, "gas": { "type": "integer", "maximum": 30000000, "minimum": 21000, "description": "optional gas limit for the cost columns (default: the simulation's gas_used)" }, "data": { "type": "string", "description": "calldata as 0x hex (omit or 0x for a plain ETH transfer); max 6 KB" }, "from": { "type": "string", "description": "the signer's wallet (0x + 40 hex): the account that would sign; its ETH balance, allowances granted and net position are checked" }, "chain": { "type": "string", "description": "optional; must be base / 8453 on this route" }, "value": { "type": "string", "description": "ETH value in wei as a decimal or 0x hex integer string (default 0)" } }, "additionalProperties": false } }, "additionalProperties": false }, "output": { "type": "object", "required": [ "type" ], "properties": { "type": { "type": "string" }, "example": { "type": "object", "required": [ "chain", "verdict", "decoded", "sim", "transfers", "net_for_from", "approvals", "risk" ], "properties": { "tx": { "type": "object" }, "sim": { "type": "object" }, "risk": { "type": "object" }, "chain": { "type": "string" }, "signer": { "type": "object" }, "decoded": { "type": "object" }, "verdict": { "type": "object" }, "chain_id": { "type": "integer" }, "precheck": { "type": "string" }, "approvals": { "type": "array" }, "transfers": { "type": "array" }, "disclaimer": { "type": "string" }, "n … (truncated) ``` ## Response schema (JSON Schema) ```json { "type": "json", "example": { "tx": { "to": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913", "data": "0x095ea7b30000000000000000000000002626664c2603336e57b271c5c0b26f421741e481ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", "from": "0xf977814e90da44bfa03b6295a0616a897441acec", "gas_limit": null, "value_eth": "0", "value_wei": "0", "data_bytes": 68 }, "sim": { "rpc": "base-rpc.publicnode.com", "method": "eth_simulateV1 (traceTransfers, validation off; funds checked separately)", "status": "0x1", "eth_usd": 2580.5, "gas_usd": 0.000865, "chain_id": 8453, "gas_used": 55785, "block_tag": "latest", "gas_price": { "basis": "effective = base fee + priority (standard tier); max = 2 x base fee + priority", "max_fee_wei": "11000000", "base_fee_wei": "5000000", "priority_wei": "1000000", "effective_wei": "6000000" }, "gas_usd_max": 0.001585, "return_data": "0x0000000000000000000000000000000000000000000000000000000000000001", "block_number": 53394126, "gas_cost_eth": "0.00000033471", "would_revert": false, "revert_reason": null, "eth_usd_source": "chainlink ETH/USD (latestRoundData)", "block_timestamp": 1793180287, "l1_data_fee_eth": "0.000000000488126494", "gas_limit_used_for_cost": 55785 }, "risk": { "ofac": { "hits": [], "available": true }, "flags": [ { "code": "UNLIMITED_APPROVAL", "label": "an unlimited allowance: the spender can move your whole balance of that token at any later time", "level": "CAUTION", "evidence": "Uniswap SwapRouter02 on USDC: $1234.56 of your balance exposed now" } ], "goplus": { "source": "GoPlus address_security (keyless)", "screened": 2, "unavailable": 0 }, "counterparties": [ { "ofac": false, "role": "to", "known": "USDC (Circle)", "goplus": { "warn": [], "block": [], "available": true }, "address": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913", "is_contract": false } ] }, "chain": "base", "signer": { "nonce": 1200, "address": "0xf977814e90da44bfa03b6295a0616a897441acec", "funds_ok": true, "balance_eth": "2.5", "needs_eth_max": "0.000000614123126494" }, "decoded": { "args": { "amount_raw": "115792089237316195423570985008687907853269984665640564039457584007913129639935", "spender_or_to": "0x2626664c2603336e57b271c5c0b26f421741e481" }, "kin … (truncated) ``` ## More - Live health (JSON, refreshed every minute): https://www.zero.xyz/c/avasis-base-transaction-pre-check-208f09a4/health.json - [Zero catalog index](https://www.zero.xyz/llms.txt) - [Other services from agents.avasis.ai](https://www.zero.xyz/host/agents.avasis.ai/llms.txt)