FreeTier Agent API

x402-services

x402_services

Read-only

3 free MCP calls per day (all tools together), then $0.0025 USDC via x402 or card credits (paid in-band: params._meta["x402/payment"]). x402 services search: Search ~8,900 live x402 pay-per-call APIs (verified/unverified by nohumans.directory probes, CC BY 4.0): name, endpoint URL, category, price, chains, status, score. Filters: q, category, chain, max_price, status=verified, limit<=100.

Input Schema

Name	Required	Description	Default
`q`	No
`chain`	No
`limit`	No
`status`	No
`category`	No
`max_price`	No

Output Schema

Name	Required	Description	Default
`total`	No
`results`	No
`sources`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 26, 2026

changedOutput schema / description

Previous value: -"Inferred from a real response captured on 2026-10-24; extra fields may appear, null-valued fields are untyped."New value: +"Inferred from a real response captured on 2026-10-26; extra fields may appear, null-valued fields are untyped."

Changed1 schema field changedOct 24, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "description": "Inferred from a real response captured on 2026-10-24; extra fields may appear, null-valued fields are untyped.",
+  "properties": {
+    "results": {
+      "items": {
+        "properties": {
+          "category": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "chains": {
+            "items": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "type": "array"
+          },
+          "currency": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "description": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "endpoint_url": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "has_sample": {
+            "type": [
+              "boolean",
+              "null"
+            ]
+          },
+          "last_probed": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "name": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "price_usd": {
+            "type": [
+              "number",
+              "null"
+            ]
+          },
+          "score": {
+            "type": [
+              "number",
+              "null"
+            ]
+          },
+          "status": {
+            "type": [
+              "string",
+              "null"
+            ]
+          }
+        },
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "sources": {
+      "items": {
+        "properties": {
+          "attribution": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "license": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "name": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "note": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "snapshot": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
+          "url": {
+            "type": [
+              "string",
+              "null"
+            ]
+          }
+        },
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "total": {
+      "type": [
+        "number",
+        "null"
+      ]
+    }
+  },
+  "type": "object"
+}

First observedOct 18, 2026

TDQS

A3.9/5.0

Behavior5/5

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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses quota (3 free MCP calls per day across all tools), pricing ($0.0025 USDC), the exact in-band payment channel (params._meta["x402/payment"]), data provenance (nohumans.directory probes, CC BY 4.0) and the verified/unverified distinction. These are exactly the operational facts an agent cannot get from structured fields.

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?

Two dense sentences with no filler, and the filter enumeration is tight. The lead position is spent on billing/quota rather than the tool's purpose, which delays the core statement slightly.

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

Completeness4/5

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

With an output schema present, return fields needn't be explained, yet the description still lists them; payment, quota and data source are all covered. The main gap is the absence of any disambiguation from the dump_x402_services sibling in a 70-tool namespace.

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 0%, so the description must carry parameter meaning; it names all six filters and adds one real constraint (limit<=100, status=verified). It still leaves q syntax, max_price units/currency, and valid category/chain values undefined, so compensation is partial.

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

Purpose4/5

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

The description gives a specific verb+resource ('Search ~8,900 live x402 pay-per-call APIs') and enumerates the returned fields, so the tool's function is unmistakable. It does not, however, distinguish itself from the sibling dump_x402_services or apis_search, which an agent could easily confuse with a search tool.

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

Usage Guidelines3/5

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

Usage is only implied through the filter list; there is no explicit statement of when to pick this over dump_x402_services or apis_search. The one useful constraint, limit<=100, hints at pagination behavior but no alternative routing is offered.

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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