Market Data · x402 · early usage

Base token sell check AT YOUR TRADE SIZE: simulates a buy of amountEth (0.001 to 10 ETH…

Base token sell check AT YOUR TRADE SIZE: simulates a buy of amountEth (0.001 to 10 ETH) and an immediate sell inside eth_call (no trade is sent) and reports the buy tax, the sell tax and the round-trip loss including price impact. Uniswap v2, v3, v4 (ETH, WE…

by base-facts.yankii.fr · discovered, not yet claimed by its owner · updated 2026-10-09

30d calls4

30d payers3

MethodPOST

Outputjson

Mirrored from Coinbase's public x402 Bazaar. The description is the provider's own text and has not been reviewed here; the payment requirements are copied as published.

What it does

Tags: base · token · honeypot · slippage · price-impact · bazaar

Call contract

Method: POST
Input: json
Output: json
Last paid call: 2026-10-09

Input example from Bazaar metadata

{
  "amountEth": "0.5",
  "token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"
}

Output example

{
  "blockNumber": "52159737",
  "disclaimer": "eth_call simulation at block 52159737: a small buy with WETH and an immediate sell on the token's deepest WETH pools. Not a guarantee: the token's code or owner can change, and some tokens treat addresses or sizes differently. Not financial advice.",
  "flags": [
    {
      "fact": "Bought with 0.01 WETH and sold straight back on uniswap-v3 pool 0x6c561B446416E1A00E8E93E221854d6eA4171372 at block 52159737 (eth_call simulation): round-trip loss 0.6%, which includes a 0.30% pool fee paid twice and any token tax.",
      "id": "sell_ok",
      "severity": "info"
    }
  ],
  "name": "USD Coin",
  "simulation": {
    "amounts": {
      "tokenReachedPool": null,
      "tokenReceived": "26912247",
      "tokenReleasedByPool": "26912247",
      "tokenSent": "26912247",
      "wethOut": "9940089592377343"
    },
    "attempts": [
      {
        "dex": "uniswap-v3",
        "fee": 3000,
        "ok": true,
        "pool": "0x6c561B446416E1A00E8E93E221854d6eA4171372",
        "wethIn": "10000000000000000"
      }
    ],
    "buyTaxPct": 0,
    "dex": "uniswap-v3",
    "fee": 3000,
    "pool": "0x6c561B446416E1A00E8E93E221854d6eA4171372",
    "roundTripLossPct": 0.6,
    "sellTaxPct": null,
    "status": "ok",
    "wethIn": "10000000000000000"
  },
  "source": "base-mainnet-rpc",
  "summary": "USDC: Simulated buy and sell on uniswap-v3: no transfer tax, round-trip loss 0.6%.",
  "symbol": "USDC",
  "token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"
}

Use with an agent

Discover. Agents find this listing with GET https://bazaar.saylorinnovations.com/discovery/search?query=…, the MCP tool search_resources, or /discovery/resources.
Inspect. Fetch /resources/35735.json for the price and payment options.
Pay. Call GET https://base-facts.yankii.fr/v1/sellcheck/size. The provider answers 402 with its payment requirements. An x402 client signs one of the options below and retries with PAYMENT-SIGNATURE.
Execute. The provider returns 200 with the data. Agent Bazaar is not in the request path and never sees your payment.

For humans

You don't need an account or an API key; you need a wallet holding a small amount of USDC on Base, and an x402-capable client (see the examples below). Call the endpoint unpaid first to see exactly what it asks for.

Pricing & payment

Price: $0.01 / request
Protocol: x402 v2
Auth: No account or API key. Pay per request.
Networks: Base
Demand: 4 calls · 3 unique payers in 30d (public x402 Bazaar data)

x402 payment requirements

Scheme	Network	Asset	Amount	Pay to	Timeout
exact	Base eip155:8453	USDC	$0.01	0x40661D56c2Bf416c5946A8b21098eaF8D33459A2	300s

accepts[] (raw JSON)

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0x40661D56c2Bf416c5946A8b21098eaF8D33459A2",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "10000",
    "amountUsd": 0.01,
    "maxTimeoutSeconds": 300
  }
]

Schemas

Output schema (JSON Schema)

{
  "properties": {
    "example": {
      "properties": {
        "blockNumber": {
          "type": "string"
        },
        "disclaimer": {
          "type": "string"
        },
        "flags": {
          "items": {
            "properties": {
              "fact": {
                "description": "The on-chain observation behind the flag",
                "type": "string"
              },
              "id": {
                "enum": [
                  "not_erc20",
                  "upgradeable_proxy",
                  "owner_not_renounced",
                  "can_mint",
                  "can_pause",
                  "can_blacklist",
                  "no_liquidity",
                  "thin_liquidity",
                  "deep_liquidity",
                  "v4_liquidity_unmeasured",
                  "v4_pool_empty",
                  "sell_ok",
                  "buy_tax",
                  "sell_tax",
                  "high_round_trip_loss",
                  "sell_reverted",
                  "buy_reverted",
                  "not_simulated"
                ],
                "type": "string"
              },
              "severity": {
                "enum": [
                  "info",
                  "warn",
                  "high"
                ],
                "type": "string"
              }
            },
            "type": "object"
          },
          "type": "array"
        },
        "name": {
          "type": [
            "string",
            "null"
          ]
        },
        "simulation": {
          "description": "eth_call buy-and-sell simulation at the verdict's block; null when the address is not an ERC20",
          "properties": {
            "amounts": {
              "properties": {
                "tokenReachedPool": {
                  "type": [
                    "string",
                    "null"
                  ]
                },
                "tokenReceived": {
                  "type": "string"
                },
                "tokenReleasedByPool": {
                  "type": "string"
                },
                "tokenSent": {
                  "type": "string"
                },
                "wethOut": {
                  "type": "string"
                }
              },
              "type": "object"
            },
            "attempts": {
              "items": {
                "properties": {
                  "dex": {
                    "type": "string"
                  },
                  "fee": {
                    "type": [
                      "integer",
                      "null"
                    ]
                  },
                  "leg": {
                    "enum": [
                      "buy",
                      "sell",
                      "unknown"
                    ],
                    "type": "string"
                  },
                  "ok": {
                    "type": "boolean"
                  },
                  "pool": {
                    "type": "string"
                  },
                  "revertReason": {
                    "type": "string"
                  },
                  "wethIn": {
                    "type": "string"
                  }
                },
                "type": "object"
              },
              "type": "array"
            },
            "buyTaxPct": {
              "type": [
                "number",
                "null"
              ]
            },
            "dex": {
              "enum": [
                "uniswap-v2",
                "uniswap-v3",
                "aerodrome-volatile",
                "uniswap-v4"
              ],
              "type": "string"
            },
            "fee": {
              "description": "Uniswap fee in hundredths of a basis point (500 = 0.05%)",
              "type": [
                "integer",
                "null"
              ]
            },
            "hooks": {
              "type": "string"
            },
            "pool": {
              "type": "string"
            },
            "reason": {
              "description": "Why the simulation was not run (status not_simulated)",
              "type": "string"
            },
            "roundTripLossPct": {
              "description": "WETH lost buying and selling straight back, pool fees included",
              "type": "number"
            },
            "sellTaxPct": {
              "description": "null on Uniswap v3 (not measurable)",
              "type": [
                "number",
                "null"
              ]
            },
            "status": {
              "enum": [
                "ok",
                "sell_reverted",
                "buy_reverted",
                "not_simulated"
              ],
              "type": "string"
            },
            "wethIn": {
              "description": "WETH wei used for the simulated buy",
              "type": "string"
            }
          },
          "type": [
            "object",
            "null"
          ]
        },
        "source": {
          "type": "string"
        },
        "summary": {
          "type": "string"
        },
        "symbol": {
          "type": [
            "string",
            "null"
          ]
        },
        "token": {
          "type": "string"
        }
      },
      "type": "object"
    },
    "type": {
      "type": "string"
    }
  },
  "required": [
    "type"
  ],
  "type": "object"
}

Example shape — generated from the schema, not a captured live response

{
  "example": {
    "blockNumber": "string",
    "disclaimer": "string",
    "flags": [
      {
        "fact": "string",
        "id": "not_erc20",
        "severity": "info"
      }
    ],
    "name": "string",
    "simulation": {
      "amounts": {
        "tokenReachedPool": "string",
        "tokenReceived": "string",
        "tokenReleasedByPool": "string",
        "tokenSent": "string",
        "wethOut": "string"
      },
      "attempts": [
        {
          "dex": "string",
          "fee": 0,
          "leg": "buy",
          "ok": true,
          "pool": "string",
          "revertReason": "string",
          "wethIn": "string"
        }
      ],
      "buyTaxPct": 0,
      "dex": "uniswap-v2",
      "fee": 0,
      "hooks": "string",
      "pool": "string",
      "reason": "string",
      "roundTripLossPct": 0,
      "sellTaxPct": 0,
      "status": "ok",
      "wethIn": "string"
    },
    "source": "string",
    "summary": "string",
    "symbol": "string",
    "token": "string"
  },
  "type": "string"
}

Examples

curl

curl "https://base-facts.yankii.fr/v1/sellcheck/size"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

JavaScript

const res = await fetch("https://base-facts.yankii.fr/v1/sellcheck/size");
if (res.status === 402) {
  const { accepts } = await res.json();
  // pay one of accepts[] via an x402 client, then retry with the payment header
}

Python

import httpx
res = httpx.get("https://base-facts.yankii.fr/v1/sellcheck/size")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header

Details

Provider: base-facts.yankii.fr
Endpoint: https://base-facts.yankii.fr/v1/sellcheck/size
Machine-readable: /resources/35735.json