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by io.github.Blackwood-State
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x402 endpoint check

blackwood_x402_check
Read-onlyIdempotent

Use when you need an x402 endpoint check or x402 endpoint test, or to validate x402 endpoint listings before paying or integrating. Do not use for actually paying the endpoint, or endpoints behind authentication. Returns JSON with an x402 check of an endpoint without paying: whether it answers 402, its payment options (scheme, network, asset, amount, payTo), Bazaar metadata and problems found for 0.007 USDC per call. Typical response time 2500 ms (p95). Category: Infrastructure.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "url": "<url>"
    },
    "name": "blackwood_x402_check"
  }
}

Input Schema

NameRequiredDescriptionDefault
urlYesPublic http(s) URL of the x402 endpoint, e.g. https://x402.org/protected
bodyNoJSON body to send with POST, e.g. {"url": "https://example.com"} (no payment is ever attached)
methodNoHTTP method of the endpoint (GET when omitted)
response_formatNoconcise (the default when omitted) keeps the JSON short: long fields such as base64 images or audio come back as separate image/audio content blocks and other long strings are cut with a marker; detailed returns the full JSON

Output Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedOutput schema / anyOf
      Previous value: -[
-  {
-    "additionalProperties": false,
-    "properties": {
-      "accepts": {
-        "items": {
-          "additionalProperties": false,
-          "properties": {
-            "amount": {
-              "type": [
-                "string",
-                "null"
-              ]
-            },
-            "amountUsd": {
-              "type": [
-                "number",
-                "null"
-              ]
-            },
-            "asset": {
-              "type": [
-                "string",
-                "null"
-              ]
-            },
-            "maxTimeoutSeconds": {
-              "type": [
-                "number",
-                "null"
-              ]
-            },
-            "network": {
-              "type": [
-                "string",
-                "null"
-              ]
-            },
-            "payTo": {
-              "type": [
-                "string",
-                "null"
-              ]
-            },
-            "scheme": {
-              "type": [
-                "string",
-                "null"
-              ]
-            }
-          },
-          "required": [
-            "scheme",
-            "network",
-            "asset",
-            "amount",
-            "amountUsd",
-            "payTo",
-            "maxTimeoutSeconds"
-          ],
-          "type": "object"
-        },
-        "type": "array"
-      },
-      "bazaar": {
-        "additionalProperties": false,
-        "properties": {
-          "inputSchema": {
-            "type": "boolean"
-          },
-          "outputSchema": {
-            "type": "boolean"
-          },
-          "present": {
-            "type": "boolean"
-          }
-        },
-        "required": [
-          "present",
-          "inputSchema",
-          "outputSchema"
-        ],
-        "type": "object"
-      },
-      "checkedAt": {
-        "type": "string"
-      },
-      "finalUrl": {
-        "type": "string"
-      },
-      "problems": {
-        "items": {
-          "type": "string"
-        },
-        "type": "array"
-      },
-      "resource": {
-        "anyOf": [
-          {
-            "additionalProperties": false,
-            "properties": {
-              "description": {
-                "type": [
-                  "string",
-                  "null"
-                ]
-              },
-              "mimeType": {
-                "type": [
-                  "string",
-                  "null"
-                ]
-              },
-              "url": {
-                "type": [
-                  "string",
-                  "null"
-                ]
-              }
-            },
-            "required": [
-              "url",
-              "description",
-              "mimeType"
-            ],
-            "type": "object"
-          },
-          {
-            "type": "null"
-          }
-        ]
-      },
-      "status": {
-        "type": "number"
-      },
-      "url": {
-        "type": "string"
-      },
-      "version": {
-        "type": [
-          "number",
-          "null"
-        ]
-      },
-      "x402": {
-        "type": "boolean"
-      }
-    },
-    "required": [
-      "url",
-      "finalUrl",
-      "status",
-      "x402",
-      "version",
-      "resource",
-      "accepts",
-      "bazaar",
-      "problems",
-      "checkedAt"
-    ],
-    "type": "object"
-  },
-  {
-    "description": "x402 PaymentRequired (returned with isError when payment is needed)",
-    "properties": {
-      "accepts": {
-        "items": {
-          "type": "object"
-        },
-        "type": "array"
-      },
-      "error": {
-        "type": "string"
-      },
-      "extensions": {
-        "type": "object"
-      },
-      "resource": {
-        "type": "object"
-      },
-      "x402Version": {
-        "type": "integer"
-      }
-    },
-    "required": [
-      "x402Version",
-      "accepts"
-    ],
-    "type": "object"
-  }
-]New value: +[
+  {
+    "additionalProperties": false,
+    "properties": {
+      "accepts": {
+        "items": {
+          "additionalProperties": false,
+          "properties": {
+            "amount": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "amountUsd": {
+              "type": [
+                "number",
+                "null"
+              ]
+            },
+            "asset": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "maxTimeoutSeconds": {
+              "type": [
+                "number",
+                "null"
+              ]
+            },
+            "network": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "payTo": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "scheme": {
+              "type": [
+                "string",
+                "null"
+              ]
+            }
+          },
+          "required": [
+            "scheme",
+            "network",
+            "asset",
+            "amount",
+            "amountUsd",
+            "payTo",
+            "maxTimeoutSeconds"
+          ],
+          "type": "object"
+        },
+        "type": "array"
+      },
+      "bazaar": {
+        "additionalProperties": false,
+        "properties": {
+          "inputSchema": {
+            "type": "boolean"
+          },
+          "outputSchema": {
+            "type": "boolean"
+          },
+          "present": {
+            "type": "boolean"
+          }
+        },
+        "required": [
+          "present",
+          "inputSchema",
+          "outputSchema"
+        ],
+        "type": "object"
+      },
+      "checkedAt": {
+        "type": "string"
+      },
+      "finalUrl": {
+        "type": "string"
+      },
+      "next": {
+        "additionalProperties": false,
+        "description": "Suggested next paid call in the same family (call it in a loop when the task continues)",
+        "properties": {
+          "method": {
+            "enum": [
+              "GET",
+              "POST"
+            ],
+            "type": "string"
+          },
+          "sample": {
+            "description": "Free fixed sample of the whole family",
+            "type": "string"
+          },
+          "service": {
+            "description": "Service id of the suggested next paid call",
+            "type": "string"
+          },
+          "tool": {
+            "description": "MCP tool name of the same call",
+            "type": "string"
+          },
+          "url": {
+            "description": "Paid route of the next call",
+            "type": "string"
+          },
+          "useWhen": {
+            "description": "When the next call is the right one",
+            "type": "string"
+          }
+        },
+        "required": [
+          "service",
+          "tool",
+          "method",
+          "url",
+          "useWhen",
+          "sample"
+        ],
+        "type": "object"
+      },
+      "problems": {
+        "items": {
+          "type": "string"
+        },
+        "type": "array"
+      },
+      "resource": {
+        "anyOf": [
+          {
+            "additionalProperties": false,
+            "properties": {
+              "description": {
+                "type": [
+                  "string",
+                  "null"
+                ]
+              },
+              "mimeType": {
+                "type": [
+                  "string",
+                  "null"
+                ]
+              },
+              "url": {
+                "type": [
+                  "string",
+                  "null"
+                ]
+              }
+            },
+            "required": [
+              "url",
+              "description",
+              "mimeType"
+            ],
+            "type": "object"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "status": {
+        "type": "number"
+      },
+      "url": {
+        "type": "string"
+      },
+      "version": {
+        "type": [
+          "number",
+          "null"
+        ]
+      },
+      "x402": {
+        "type": "boolean"
+      }
+    },
+    "required": [
+      "url",
+      "finalUrl",
+      "status",
+      "x402",
+      "version",
+      "resource",
+      "accepts",
+      "bazaar",
+      "problems",
+      "checkedAt"
+    ],
+    "type": "object"
+  },
+  {
+    "description": "x402 PaymentRequired (returned with isError when payment is needed)",
+    "properties": {
+      "accepts": {
+        "items": {
+          "type": "object"
+        },
+        "type": "array"
+      },
+      "error": {
+        "type": "string"
+      },
+      "extensions": {
+        "type": "object"
+      },
+      "resource": {
+        "type": "object"
+      },
+      "x402Version": {
+        "type": "integer"
+      }
+    },
+    "required": [
+      "x402Version",
+      "accepts"
+    ],
+    "type": "object"
+  }
+]
  2. Added

TDQS

A4.6/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly/idempotent/non-destructive, but the description adds materially more: no payment is ever attached, a per-call cost of 0.007 USDC, a p95 latency of 2500 ms, and the shape of what is returned (402 status, payment options, Bazaar metadata, problems). Cost and timing disclosures are not derivable from the annotations and are exactly the operational context an agent needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The usage condition, exclusions, return shape, cost, and latency are all front-loaded and each carries useful information. The opening 'x402 endpoint check or x402 endpoint test' phrase is mildly redundant filler, keeping it just short of a 5.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given a rich output schema the return value needn't be re-explained, yet the description still captures the key returned fields, cost, latency, and scope limits for a paid, open-world read tool. Nothing needed to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so url, body, method, and response_format are already documented in the schema with examples and enum meanings. The description reinforces the no-payment behavior of the body but adds no parameter syntax or defaults beyond what the schema provides, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb+resource ('x402 endpoint check/test', 'validate x402 endpoint listings') and immediately frames the scope as inspection without payment, which no sibling tool overlaps with. An agent can identify the tool's function without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives explicit when-to-use ('validate x402 endpoint listings before paying or integrating') and when-not ('do not use for actually paying the endpoint, or endpoints behind authentication'). Both positive and negative conditions are stated, so routing is unambiguous.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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