x402 Pay — USDC API Payment Helper

Check Payment

check_payment

Read-onlyIdempotent

Inspect a public HTTPS URL for a fresh x402 v2 HTTP 402 challenge using an unsigned GET with a 10-second network timeout and no redirect following. Returns validated payTo, asset, network, atomic amount, resource and maxTimeoutSeconds; incomplete or non-x402 responses return challenge=null and a reason. Does not sign, settle or verify receipts. Fresh requirements override documented receiver hints; inspect canonical_receiver_match before choosing to pay.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`url`	Yes	Full public HTTPS URL to inspect with an unsigned GET. No payment headers; redirects, credentials and private network targets are rejected.

Output Schema

TableJSON Schema

Name	Required	Description
`reason`	No
`is_x402`	Yes	True only for HTTP 402 with complete validated x402 v2 requirements.
`challenge`	Yes	Fresh validated requirements, or null. No synthetic defaults are inserted.
`http_status`	Yes	Observed HTTP status; zero means no HTTP response was received.
`raw_headers`	No	Allowlisted response headers only; never cookies or authentication headers.
`payment_sent`	Yes
`missing_fields`	No
`canonical_receiver_match`	No	Comparison with documented SML receiver; a mismatch never rewrites upstream requirements.

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedOct 13, 2026

addedInput schema / properties / url / description

Added value: +"Full public HTTPS URL to inspect with an unsigned GET. No payment headers; redirects, credentials and private network targets are rejected."

addedInput schema / properties / url / format
```
Added value: +"uri"
```
addedInput schema / properties / url / pattern
```
Added value: +"^https://"
```

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "allOf": [
+    {
+      "else": {
+        "properties": {
+          "challenge": {
+            "type": "null"
+          }
+        }
+      },
+      "if": {
+        "properties": {
+          "is_x402": {
+            "const": true
+          }
+        }
+      },
+      "then": {
+        "properties": {
+          "challenge": {
+            "additionalProperties": false,
+            "properties": {
+              "amount": {
+                "pattern": "^[0-9]+$",
+                "type": "string"
+              },
+              "asset": {
+                "description": "Asset identifier from the fresh requirements; never replaced with a cached symbol.",
+                "minLength": 1,
+                "type": "string"
+              },
+              "maxTimeoutSeconds": {
+                "maximum": 3600,
+                "minimum": 1,
+                "type": "integer"
+              },
+              "network": {
+                "minLength": 1,
+                "type": "string"
+              },
+              "payTo": {
+                "pattern": "^0x[a-fA-F0-9]{40}$",
+                "type": "string"
+              },
+              "resource": {
+                "description": "Exact resource URL or identifier advertised by the endpoint.",
+                "minLength": 1,
+                "type": "string"
+              },
+              "scheme": {
+                "description": "Payment scheme advertised by the fresh requirement.",
+                "minLength": 1,
+                "type": "string"
+              },
+              "x402Version": {
+                "const": 2
+              }
+            },
+            "required": [
+              "x402Version",
+              "scheme",
+              "payTo",
+              "asset",
+              "network",
+              "amount",
+              "resource",
+              "maxTimeoutSeconds"
+            ],
+            "type": "object"
+          },
+          "http_status": {
+            "const": 402
+          }
+        }
+      }
+    }
+  ],
+  "properties": {
+    "canonical_receiver_match": {
+      "description": "Comparison with documented SML receiver; a mismatch never rewrites upstream requirements.",
+      "type": "boolean"
+    },
+    "challenge": {
+      "description": "Fresh validated requirements, or null. No synthetic defaults are inserted.",
+      "oneOf": [
+        {
+          "additionalProperties": false,
+          "properties": {
+            "amount": {
+              "pattern": "^[0-9]+$",
+              "type": "string"
+            },
+            "asset": {
+              "description": "Asset identifier from the fresh requirements; never replaced with a cached symbol.",
+              "minLength": 1,
+              "type": "string"
+            },
+            "maxTimeoutSeconds": {
+              "maximum": 3600,
+              "minimum": 1,
+              "type": "integer"
+            },
+            "network": {
+              "minLength": 1,
+              "type": "string"
+            },
+            "payTo": {
+              "pattern": "^0x[a-fA-F0-9]{40}$",
+              "type": "string"
+            },
+            "resource": {
+              "description": "Exact resource URL or identifier advertised by the endpoint.",
+              "minLength": 1,
+              "type": "string"
+            },
+            "scheme": {
+              "description": "Payment scheme advertised by the fresh requirement.",
+              "minLength": 1,
+              "type": "string"
+            },
+            "x402Version": {
+              "const": 2
+            }
+          },
+          "required": [
+            "x402Version",
+            "scheme",
+            "payTo",
+            "asset",
+            "network",
+            "amount",
+            "resource",
+            "maxTimeoutSeconds"
+          ],
+          "type": "object"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "http_status": {
+      "description": "Observed HTTP status; zero means no HTTP response was received.",
+      "maximum": 599,
+      "minimum": 0,
+      "type": "integer"
+    },
+    "is_x402": {
+      "description": "True only for HTTP 402 with complete validated x402 v2 requirements.",
+      "type": "boolean"
+    },
+    "missing_fields": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "payment_sent": {
+      "const": false
+    },
+    "raw_headers": {
+      "additionalProperties": {
+        "type": "string"
+      },
+      "description": "Allowlisted response headers only; never cookies or authentication headers.",
+      "type": "object"
+    },
+    "reason": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "is_x402",
+    "http_status",
+    "challenge",
+    "payment_sent"
+  ],
+  "type": "object"
+}

First observedSep 5, 2026

TDQS

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