402Signal

Official

Overview Schema Source Related Servers Discussions Admin

preview

Read-onlyIdempotent

Find paid API endpoints by capability without paying or contacting sellers. Returns catalog claims and prior observations; use validate for a live check before paying.

Instructions

Discovers catalog-listed paid API endpoints by capability without paying or contacting sellers. Returns claimed listings and earlier observations; not_probed=true means no new live check. Results may be incomplete.

Free and read-only: no fee, no seller contact, nothing recorded; safe to repeat. It queries the current upstream catalogs and the local shadow catalog. Use validate for a free readiness check of one listed URL, and check for a fresh paid observation or a signed receipt before paying.

Pass a nonblank need (capability), not a URL; a URL in need finds nothing. networks is a hard allowlist and prefer_network only orders the results within it; an empty or unrecognized networks value restricts to nothing rather than widening to every network. Seller-written fields in hits are catalog claims, not observations.

Input Schema

TableJSON Schema

Name	Required	Description
`need`	Yes	Nonblank capability to search for, such as weather or web search. Searches catalogs; does not probe a URL.
`networks`	No	Hard policy lock. Restricts searchable rails to this set. Unlike prefer_network, this is not a ranking preference.
`prefer_network`	No	Weak ranking preference only. Ranks this seller network first but still searches and selects across all supported networks. Not a filter. Use networks for a hard policy lock. Observed networks: base, solana, algorand and the EVM chains polygon, arbitrum, monad, worldchain, xlayer, bnb, hyperevm, ethereum, optimism, avalanche, tempo, sei, celo, robinhood (CAIP-2 ids such as eip155:137 are accepted); the checking fee itself is paid on base, solana or algorand.

Output Schema

TableJSON Schema

Name	Required	Description
`hits`	No	Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts.
`need`	No
`total`	No
`cached_s`	No
`displayed`	No
`freshness`	No
`truncated`	No
`not_probed`	No
`miss_reason`	No
`discovery_via`	No
`discovery_matches`	No
`discovery_exhaustive`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedv0.1.5Sep 15, 2026

changedInput schema / properties / networks / items / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand",
-  "polygon",
-  "arbitrum",
-  "monad",
-  "worldchain",
-  "xlayer",
-  "bnb",
-  "hyperevm",
-  "ethereum",
-  "optimism",
-  "avalanche",
-  "tempo"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche",
+  "tempo",
+  "sei",
+  "celo",
+  "robinhood"
+]

changedInput schema / properties / prefer_network / description

Previous value: -"Weak ranking preference only. Ranks this seller network first but still searches and selects across all supported networks. Not a filter. Use networks for a hard policy lock. Observed networks: base, solana, algorand and the EVM chains polygon, arbitrum, monad, worldchain, xlayer, bnb, hyperevm, ethereum, optimism, avalanche (CAIP-2 ids such as eip155:137 are accepted); the checking fee itself is paid on base, solana or algorand."New value: +"Weak ranking preference only. Ranks this seller network first but still searches and selects across all supported networks. Not a filter. Use networks for a hard policy lock. Observed networks: base, solana, algorand and the EVM chains polygon, arbitrum, monad, worldchain, xlayer, bnb, hyperevm, ethereum, optimism, avalanche, tempo, sei, celo, robinhood (CAIP-2 ids such as eip155:137 are accepted); the checking fee itself is paid on base, solana or algorand."

changedInput schema / properties / prefer_network / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand",
-  "polygon",
-  "arbitrum",
-  "monad",
-  "worldchain",
-  "xlayer",
-  "bnb",
-  "hyperevm",
-  "ethereum",
-  "optimism",
-  "avalanche",
-  "tempo"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche",
+  "tempo",
+  "sei",
+  "celo",
+  "robinhood"
+]

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
+]

Changed4 schema fields changedv0.1.4Sep 13, 2026

changedInput schema / properties / networks / items / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche",
+  "tempo"
+]

changedInput schema / properties / prefer_network / description

Previous value: -"Weak ranking preference only. Ranks this pay-in rail first but still searches and selects across all supported rails. Not a filter. Use networks for a hard policy lock."New value: +"Weak ranking preference only. Ranks this seller network first but still searches and selects across all supported networks. Not a filter. Use networks for a hard policy lock. Observed networks: base, solana, algorand and the EVM chains polygon, arbitrum, monad, worldchain, xlayer, bnb, hyperevm, ethereum, optimism, avalanche (CAIP-2 ids such as eip155:137 are accepted); the checking fee itself is paid on base, solana or algorand."

changedInput schema / properties / prefer_network / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche",
+  "tempo"
+]

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",
+  "authorization_used",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  null
+]

Changed1 schema field changedv0.1.1Sep 9, 2026

changedInput schema / properties / need / description

Previous value: -"What to look up in the cache."New value: +"Nonblank capability to search for, such as weather or web search. Searches catalogs; does not probe a URL."

First observedv0.1.0Sep 8, 2026

TDQS

A4.9/5.0

Behavior5/5

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

Annotations cover safety (readOnly, idempotent, openWorld, non-destructive), yet the description still adds substantive context: no fee, no seller contact, nothing recorded, safe to repeat, results may be incomplete, not_probed=true means no new live check, and seller-written fields are catalog claims rather than observations. That is behavioral disclosure well beyond the annotation bar.

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?

Purpose and safety are front-loaded, and each sentence carries distinct information (routing, parameter caveats, claim-vs-observation warning). It is dense and slightly long across three blocks, but no sentence is filler.

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?

An output schema exists, so return structure need not be explained, yet the description still decodes the key result flag (not_probed) and the reliability caveat about claimed fields. For a discovery tool with two siblings and three parameters, nothing an agent needs 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.

Parameters5/5

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

Schema coverage is already 100%, but the description adds semantics the schema lacks: 'need' is a capability not a URL and a URL finds nothing; 'networks' is a hard allowlist whose empty/unrecognized value restricts to nothing rather than widening; 'prefer_network' only orders results within it. These are real distinctions, not restatements, and they prevent predictable misuse.

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 (discovers) plus resource (catalog-listed paid API endpoints) and scope (by capability, without paying or contacting sellers). The distinction from siblings check and validate is immediately legible, so an agent can separate the three without opening a 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?

Names both alternatives explicitly and the condition that selects each: 'Use validate for a free readiness check of one listed URL, and check for a fresh paid observation or a signed receipt before paying.' This is explicit when/when-not/alternative routing.

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

Deploy Server