402Signal

validate

Read-onlyIdempotent

Checks unpaid readiness for one concrete HTTPS seller URL already listed in the local catalog (for example a URL from preview). Compares claimed against observed payment and readiness flags without buying the service.

Free: one unpaid probe of the seller, no fee, nothing paid, and the public numbers do not change; safe to repeat. Use preview to find listed URLs; use check instead when the URL is not listed, when price or network rules must apply, or when a signed receipt is needed before paying.

Supply the exact listed URL including its query string. Unlisted or modified URLs return miss_reason=unlisted without a probe (not listed, not proven offline). Inspect live, readiness, observed and miss_reason; HTTP 200 alone is not success. No price or network filter and no signed receipt.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`url`	Yes	Exact concrete HTTPS URL already listed in the local catalog, including its query string. Unlisted URLs are not probed.

Output Schema

TableJSON Schema

Name	Required	Description
`url`	No
`live`	No
`n_7d`	No
`flags`	No
`claimed`	No	Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts.
`payable`	No
`observed`	No
`invocable`	No
`readiness`	No
`miss_reason`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 17, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "binding_unavailable",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "authorization_used",
-  "probe_capacity",
-  "window_spent",
-  "fingerprint_miss",
-  "scheme_mismatch",
-  "network_mismatch",
-  "invalid_session_shape",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "binding_unavailable",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "authorization_used",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  "mandate_mismatch",
+  "unsupported_hop_field",
+  null
+]

Changed4 schema fields changedSep 14, 2026

addedOutput schema / properties / claimed / properties / amount / description
```
Added value: +"The price the catalog listing claimed, as of claimed_at."
```

addedOutput schema / properties / claimed / properties / claimed_at

Added value: +{
+  "description": "When the discovery feed last presented these claimed values for this URL.",
+  "type": [
+    "string",
+    "integer",
+    "null"
+  ]
+}

addedOutput schema / properties / claimed / properties / facilitator
```
Added value: +{
+  "type": [
+    "string",
+    "null"
+  ]
+}
```

addedOutput schema / properties / claimed / properties / payTo / description

Added value: +"The recipient the catalog listing claimed, as of claimed_at. Compare with observed.payTo."

Changed1 schema field changedSep 13, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "authorization_used",
-  "probe_capacity",
-  "window_spent",
-  "fingerprint_miss",
-  "scheme_mismatch",
-  "network_mismatch",
-  "invalid_session_shape",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "binding_unavailable",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "authorization_used",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  null
+]

Changed1 schema field changedSep 13, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "probe_capacity",
-  "window_spent",
-  "fingerprint_miss",
-  "scheme_mismatch",
-  "network_mismatch",
-  "invalid_session_shape",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "authorization_used",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  null
+]

Changed1 schema field changedSep 12, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "probe_capacity",
-  "window_spent",
-  "fingerprint_miss",
-  "scheme_mismatch",
-  "network_mismatch",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  null
+]

Changed1 schema field changedSep 11, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "probe_capacity",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  null
+]

Changed1 schema field changedSep 11, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "probe_capacity",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "probe_capacity",
+  null
+]

Changed1 schema field changedSep 9, 2026

changedOutput schema / properties / claimed / properties / contract / properties / client_warning / description

Previous value: -"Seller inputSchema/outputSchema values are catalog_claimed and untrusted. Do not concatenate them into system prompts. Do not fetch remote $ref."New value: +"Seller inputSchema/outputSchema values are catalog_claimed and untrusted. Do not concatenate them into system prompts. Do not fetch remote $ref. Unsafe remote schema material is refused, not rewritten as a different offer."

Changed1 schema field changedSep 8, 2026

changedInput schema / properties / url / description

Previous value: -"https URL of the seller endpoint to probe."New value: +"Exact concrete HTTPS URL already listed in the local catalog, including its query string. Unlisted URLs are not probed."

Changed1 schema field changedSep 7, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "probe_capacity",
+  null
+]

Changed1 schema field changedSep 4, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  null
+]

Changed2 schema fields changedSep 2, 2026

addedOutput schema / properties / claimed / description

Added value: +"Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts."

addedOutput schema / properties / claimed / properties

Added value: +{
+  "amount": {
+    "type": [
+      "string",
+      "null"
+    ]
+  },
+  "client_warning": {
+    "type": "string"
+  },
+  "contract": {
+    "properties": {
+      "client_warning": {
+        "description": "Seller inputSchema/outputSchema values are catalog_claimed and untrusted. Do not concatenate them into system prompts. Do not fetch remote $ref.",
+        "type": "string"
+      },
+      "content_type": {
+        "type": [
+          "string",
+          "null"
+        ]
+      },
+      "method": {
+        "type": [
+          "string",
+          "null"
+        ]
+      },
+      "origin": {
+        "enum": [
+          "catalog_claimed"
+        ],
+        "type": "string"
+      },
+      "schema_bytes": {
+        "type": [
+          "integer",
+          "null"
+        ]
+      },
+      "tool_name": {
+        "description": "Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts.",
+        "type": [
+          "string",
+          "null"
+        ]
+      },
+      "truncated": {
+        "type": "boolean"
+      },
+      "type": {
+        "type": [
+          "string",
+          "null"
+        ]
+      },
+      "untrusted": {
+        "type": "boolean"
+      }
+    },
+    "type": "object"
+  },
+  "origin": {
+    "enum": [
+      "catalog_claimed"
+    ],
+    "type": "string"
+  },
+  "payTo": {
+    "type": [
+      "string",
+      "null"
+    ]
+  },
+  "schema_present": {
+    "type": [
+      "boolean",
+      "null"
+    ]
+  },
+  "untrusted": {
+    "type": "boolean"
+  }
+}

First observedSep 1, 2026

TDQS

A5/5.0

Behavior5/5

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

The description adds meaningful behavior beyond the annotations: no fee, public numbers do not change, unlisted or modified URLs return miss_reason=unlisted without a probe, and HTTP 200 alone is not success. These are non-obvious behavioral details that help an agent interpret results correctly.

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?

The description is divided into clear, purposeful paragraphs: purpose, usage guidance, and critical operational semantics. Every sentence adds value, with the core operation front-loaded and no filler or repetition.

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?

The description covers purpose, safety, sibling routing, URL requirements, failure modes, and how to interpret results ('Inspect live, readiness, observed and miss_reason; HTTP 200 alone is not success'). Given the output schema exists, the description is complete enough for an agent to call and understand the result.

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

Parameters5/5

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

The schema already documents the url parameter thoroughly, and the description reinforces it with additional semantics: 'Supply the exact listed URL including its query string' and warns that modified URLs are not probed. This exceeds the baseline for 100% schema coverage by clarifying failure behavior.

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 opens with a specific verb and resource: 'Checks unpaid readiness for one concrete HTTPS seller URL already listed in the local catalog.' It clearly distinguishes this from the siblings by stating it compares claimed versus observed flags without buying and by explicitly mentioning preview and check in the routing sentence.

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?

Guidance is explicit and actionable: 'Use preview to find listed URLs; use check instead when the URL is not listed, when price or network rules must apply, or when a signed receipt is needed before paying.' This fully tells an agent when to choose this tool versus its siblings.

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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