x402 Pay — USDC API Payment Helper

List Paid Apis

list_paid_apis

Read-onlyIdempotent

List paid API operations declared by the live SqueezeOS OpenAPI document, bounded by limit. Returns method, path, job and advertised price. Use for route selection, then inspect that resource's fresh 402 challenge; listed prices do not authorize payment.

Input Schema

Name	Required	Description	Default
`limit`	No	Maximum number of declared paid operations to return; not an exhaustive catalog count.

Output Schema

Name	Required	Description	Default
`ok`	Yes
`count`	Yes
`source`	Yes
`operations`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 13, 2026

addedInput schema / properties / limit / description

Added value: +"Maximum number of declared paid operations to return; not an exhaustive catalog count."

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "properties": {
+    "count": {
+      "type": "integer"
+    },
+    "ok": {
+      "type": "boolean"
+    },
+    "operations": {
+      "items": {
+        "additionalProperties": true,
+        "properties": {
+          "advertised_price": {},
+          "job": {},
+          "method": {
+            "type": "string"
+          },
+          "path": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "method",
+          "path",
+          "job",
+          "advertised_price"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "source": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "ok",
+    "source",
+    "count",
+    "operations"
+  ],
+  "type": "object"
+}

First observedSep 5, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds genuinely non-obvious context: the catalog comes from a live document, results are bounded, and listed prices do not authorize payment. That payment caveat materially affects downstream behavior, though nothing is said about rate limits or catalog staleness.

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

Conciseness5/5

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

Three tight sentences, front-loaded with what the tool lists and what it returns, followed by usage and the payment caveat. No filler or restatement of the title.

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?

For a single-parameter read tool with a full schema, complete annotations and an output schema, the description supplies everything needed: data source, bound, return shape and the critical caveat that listed prices are not authorization to pay.

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 coverage is 100% and the single limit parameter is documented with default, min, max and a note that it is not a catalog count. The description's "bounded by limit" adds no syntax or format detail beyond what the schema already 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?

States a specific verb and resource (list paid API operations) and an explicit source (the live SqueezeOS OpenAPI document), plus the returned fields (method, path, job, advertised price). An agent can distinguish it from check_payment/payment_info/x402_inspect_challenge without opening any schema.

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

Usage Guidelines4/5

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

"Use for route selection, then inspect that resource's fresh 402 challenge" gives a clear when-to-use and names the follow-up step that corresponds to the sibling x402_inspect_challenge. It stops short of naming the alternative tool directly or stating exclusions, so it is strong but not fully explicit routing.

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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