x402-list-mcp

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

Annotations only declare the generic safety profile (readOnly=false, openWorld=true, idempotent=false, destructive=false); the description adds far more: the two-call challenge/retry flow, that the server holds no keys and never signs or settles, non-refundable probe fees, no-charge-if-assessment-fails, and reading amount from accepts[0]. The only small gap is that it doesn't say whether repeated identical calls are billed repeatedly, which is implied but not stated. No contradiction with annotations: spending money with no signing/settling is consistent with readOnly=false, destructive=false, idempotent=false.

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

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

Front-loaded with the selection condition before the mechanics, and nearly every clause carries decision-relevant information. It is a single dense block of ~250 words; splitting the payment flow, probe behavior, and caveats into separate sentences/sections would improve scanability without cutting content.

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

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

No output schema exists, yet the description specifies what is returned (the report, a base64 PAYMENT-RESPONSE settlement receipt, and an optional probe_report with verdict and truncated extracts, never the verbatim third-party body). For a two-call paid tool with a nested probe object, 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.

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

Schema coverage is already 100%, so the baseline is 3, but the description adds real meaning: payment_signature_b64 is a retry-only argument produced by signing accepts[0], and probe changes the price to $0.25 plus the endpoint price X and adds a probe_report block. It doesn't restate field limits, which the schema already handles.

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

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

States a specific verb and resource (buys one fresh AI assessment of a shortlist, priced in USDC) and explicitly distinguishes itself from x402_search_services, x402_find_best_service, and x402_get_service. An agent can tell exactly what it gets here versus the free siblings 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.

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

Gives an explicit precondition chain: 2-8 finalists held, stored fields insufficient for the stated need, and cost of a wrong choice exceeding a quarter. Names the alternative path for the non-qualifying case (free cached reads via x402_get_service), so both when-to-use and when-not-to-use are covered.

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

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

Beyond the readOnlyHint annotation, it discloses non-obvious traits an agent could not infer: payTo values are masked by design so the feed reports that a payout address changed but never the address, and prices are atomic token amounts rather than dollars. It also states ordering (most recent first) and that the tool is free.

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

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

The usage trigger is front-loaded before the payload description and the caveats are grouped at the end, which is good structure. It is somewhat dense in a single paragraph and briefly repeats annotation-derived facts ('Free and read-only') and the type enum already in the schema.

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

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

For a paginated read tool with no output schema, the description supplies what the schema cannot: the shape of returned events (payTo/price/schema changes), sort order, units, and the masking caveat, while pagination mechanics are handled by the schema. An agent can call this correctly without further information.

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

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

Schema description coverage is 100%, so every parameter including days, type, service, page and per_page is already fully documented in the schema. The description restates the filters (service slug, type, days 1-365 default 90) and omits pagination parameters entirely, so it adds essentially no meaning beyond the structured data — baseline 3.

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

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

The description states a specific resource (the monitor's log of payTo, price and 402-schema changes on listed services) and enumerates the exact three event types, which cleanly separates it from siblings like x402_get_service or x402_check_health that report current state rather than change history.

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

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

It gives explicit trigger conditions — call before trusting cached service data and immediately after an unexplained payment failure — which tell the agent both when to reach for this feed and what it substitutes for (stale cache assumptions). No alternative tool is needed for the same job.

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

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

The annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds real value by stating 'No money fields' (meaningful in a payment protocol) and enumerating what each mode returns, but it does not disclose rate limits, auth requirements, or how large the include_services=true payload could be.

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

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

It is compact and front-loads the when-to-call guidance before the mode breakdown. The telegraphic fragment style ('is this service up right now') is dense but every clause conveys distinct information about inputs or outputs.

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

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

With no output schema, the description carries the return-value burden and does so for both modes, listing status counts, uptime windows, response time, consecutive failures, and daily snapshots. The main gap is the lack of any mention of pagination or size limits when include_services=true attaches every row.

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

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

Schema coverage is 100%, so the baseline is 3, but the description goes beyond the schema by explaining the slug/no-slug mode split and explicitly tying include_services=true to attaching 'every row'. It adds the operational meaning of the parameters rather than restating them.

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

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

The description states a specific purpose (is this service up right now) and clearly separates its two modes: directory snapshot with five status counts versus single-service status with uptime windows. It distinguishes itself functionally by noting 'No money fields', though it never names sibling tools like x402_get_service or x402_assess_services to sharpen the boundary.

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

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

It gives explicit triggering conditions: 'Call this before you send a payment, or right after a call unexpectedly failed.' That is clear when-to-use context, but there are no exclusions or named alternatives, so the agent must infer why this differs from x402_get_service or x402_assess_services.

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

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

Annotations already cover read-only/open-world, yet the description adds substantial non-structured context: the 'on-chain' vs 'listed' verification flag semantics, that *_24h covers today UTC so far and resets at 00:00 UTC, that volume is decimal USD, and a recommendation to prefer 7d. These are genuine behavioral caveats an agent cannot get from the schema.

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

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

Front-loaded with the routing condition, then return contents, then caveats — a sensible ordering. It is dense and long-ish, but nearly every clause carries information; only the 'more than 30 facilitators' detail is borderline padding.

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

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

No output schema exists, and the description fully describes the return shape: per-facilitator volume and tx counts across four timeframes, a verification flag, optional daily timeseries, and optional per-chain breakdown. Combined with the caveats, an agent has everything needed to call and interpret it correctly.

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

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

Schema coverage is 67%, and the description compensates: it explains the 90-day timeseries cap, the per-chain breakdown, the timeframe caveat about today-UTC ordering, and advises preferring 7d. Page/per_page are left entirely to the schema with no semantic help, which keeps it below a 5.

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

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

States a specific verb+resource: returns on-chain-verified settlement volume and transaction counts per x402 facilitator. It explicitly scopes the tool to the 'rail rather than the service', which cleanly separates it from the service-level siblings (x402_assess_services, x402_get_service).

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

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

The opening clause gives a clear selection rule ('when the question is about the rail rather than the service') and the caveat 'PER-FACILITATOR, never per-service' reinforces when not to use it. It does not name the specific sibling to use instead, so routing is implied rather than explicit.

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

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

Annotations already declare readOnlyHint and openWorldHint, and the description does not contradict them. The description adds details on ranking methodology but does not explicitly mention that the tool makes no modifications or that results may change (open-world). Given the annotations cover the key behavioral aspects, a neutral score is appropriate.

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

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

The description is unusually long and repetitive, with multiple sentences restating ranking weights and output fields. It lacks a clear front-loaded summary; the first sentence is confusing and the subsequent paragraphs ramble. A concise version would improve readability without losing essential information.

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

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

Given the absence of an output schema, the description attempts to describe the response structure (ranking_version, need_blind_ranking, units map) and the meaning of include_facilitator_context. However, it leaves ambiguities (e.g., what 'units map' keys are, how caveats apply) and does not fully compensate for the lack of a formal output schema.

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

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

The schema already provides complete descriptions for all 8 parameters. The description adds context on ranking criteria and mentions some parameters indirectly (e.g., 'price cap' for max_price_usd), but it does not meaningfully enhance parameter understanding beyond the schema. The addition of the 'units map' is unclear and could be considered more about output than input semantics.

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

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

The description clarifies that this tool returns ranked service recommendations based on a free-text need and optional filters, distinguishing it from a simple search. However, the phrase 'free ranking step' is ambiguous (likely 'first ranking step' or 'the ranking step'), and the long sentence structure initially obscures the core purpose.

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

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

The description gives a broad trigger ('when you have a need in words') but does not explicitly compare with sibling tools (e.g., when to use x402_search_services vs. x402_find_best_service). No 'use X instead' guidance is provided, leaving the agent to infer the tool's relationship to others.

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

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

Annotations only cover readOnly and openWorld. The description adds substantial context beyond them: the pay_to divergence warning surfaced at top level and endpoints[].pay_to_divergence, the meaning of include_series and its cost, and the crucial caveat that the price field is atomic token units rather than dollars. This is exactly the kind of behavior-shaping detail 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.

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

Front-loads the purpose and the when-to-call condition in the first clause before piling on the returned fields. It is dense and slightly run-on across the warnings and units sentences, but every sentence carries actionable information, so little is wasted.

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

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

No output schema exists, so the description carries the full burden and meets it: it describes the record's contents, optional series, the conditional warnings path, and the units convention. An agent knows what it will get and how to read it without guessing.

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

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

Schema coverage is 100%, so the baseline is 3. The description reinforces include_series by tying it to concrete value ('90 daily points of on-chain volume and distinct buyers'), which slightly overlaps the schema but clarifies intent. The units-map note is about interpreting output, not the slug/include_series params, so it doesn't lift this dimension further.

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

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

States a specific verb and resource (fetch the full service record behind a directory row) and enumerates what it contains: live status, uptime windows, response time, networks/settlement asset, priced endpoints, assessment block. The framing 'once you hold a slug' cleanly separates it from search/find_best siblings that the agent uses before it has a slug.

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

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

Gives an explicit trigger: call once you hold a slug and are deciding whether to commit. This implicitly routes the agent away from x402_search_services / x402_find_best_service, which are the pre-slug tools. No explicit when-not or named alternative, so it falls short of a 5.

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

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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered; the description adds real value beyond them by disclosing page size limits ('up to 100 compact summaries a page'), the compact-vs-full payload tradeoff that avoids truncation, and the subtle signable semantics including the case where an unmeasured service matches neither value.

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

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

Three sentences, front-loaded with the 'call this first' trigger, then capabilities, then the handoff. No filler and no repetition of the schema's enum values beyond what is needed to signal the available axes.

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

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

With no output schema, the description carries the return-value burden and does so ('price in decimal USD, uptime, status, verification', paginated to 100), plus a clear next-step pointer. Nothing an agent needs to call a 10-parameter read-only search correctly is missing.

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

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

Schema coverage is 100%, so the baseline is 3; the description still earns credit by summarizing the filter axes (query, category, network, live status, signable), the four sort orders, and the field-detail switch in prose. It adds interpretation ('price in decimal USD') rather than duplicating the enum lists verbatim.

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

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

States a concrete verb and resource ('narrows the directory of listed services to candidates') plus the exact scope of what can be filtered and sorted. It explicitly routes the follow-up to x402_get_service for full records, so an agent can separate it from that sibling 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.

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

'Your first call when you do not know which x402 service exists for a job' is explicit about when to reach for it, and the closing sentence names the next step (x402_get_service). It stops short of contrasting with find_best_service or assess_services, which are the other plausible choices for a service-discovery task.

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