402Signal

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

No annotations are provided, so the description bears the full behavioral burden. It usefully discloses that the tool performs no probing, incurs no charge, operates over upstream catalogs plus a local shadow, and returns not_probed:true. It does not cover auth, failure modes, or rate limits, but the cost and side-effect profile is clearly conveyed.

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?

Two dense sentences deliver the operational definition, key behavior, return-field names, cost/probe characteristics, and routing to an alternative. There is no filler or redundant restatement of the tool name.

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 a full input schema and an output schema present, the description does not need to explain return structures or parameter syntax. It covers what the tool is, what it returns at a high level, that it is non-probing and non-charging, and when to use route instead. Minor ambiguity remains around the phrase 'Pay tools/call route,' but overall the definition is complete enough for correct selection and invocation.

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%, and the schema already documents the distinction between networks as a hard policy lock and prefer_network as a weak ranking preference. The description adds no parameter-specific details beyond the schema, so the baseline score of 3 applies.

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 opens with a specific operation ('Request-time catalog preflight over upstream catalogs plus a local shadow') and names the resource and return highlights. It also distinguishes itself from the sibling route tool by explicitly noting it does not probe, making the tool's purpose and scope immediately clear.

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 states the tool's preflight role and explicitly routes live-probe needs to the route sibling: 'Pay tools/call route for a live probe.' It also discloses that this tool 'does not probe and does not charge,' giving an agent a clear basis for choosing it over the live-probe alternative.

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?

With no annotations, the description carries the burden and does disclose key behaviors: the $0.003 charge only on valid live routes, typed misses not settled, seller payment separate, wallet custody retained by the agent, and routing evidence written to the PQ Trust log. It does not explicitly mention that network probes are performed or that the tool is not a payment execution, leaving some behavioral ambiguity.

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 a compact paragraph that front-loads the core action and then covers pricing, settlement, custody, and evidence. Some clauses duplicate parameter descriptions (route binding) and are arguably unnecessary, but overall it is economical and readable.

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 23-parameter tool with no annotations, the description provides useful high-level context (networks, billing, evidence, custody) but omits the overall workflow, explicit side effects (probing external URLs), and any guidance on when to use this tool rather than siblings. The presence of an output schema mitigates the return-value gap, but the missing usage and side-effect context keeps this below complete.

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 the baseline is 3. The description only echoes one parameter (require_route_binding) and adds no new meaning for the other 22 parameters. Parameter semantics are therefore fully covered by the schema, not by the description.

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 concrete action ('checks x402 routes') with a clear scope (Base, Solana, Algorand) and context ('before spending'). However, it doesn't explicitly say what the tool returns or how it differs from the sibling tools preview and validate, so the purpose is clear but not fully differentiated.

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?

There is no guidance about when to call route versus preview or validate. The only hint is 'before spending,' which is implicit and not actionable enough to select this tool over alternatives. It also doesn't state prerequisites or conditions that should trigger a call.

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?

With no annotations provided, the description carries the full burden of disclosure, and it does well by stating it is unpaid, fail-closed against SSRF, returns readiness/claimed-vs-observed/flags, and does not charge. It does not detail network side effects or auth requirements, but for a simple probe tool the disclosed behavior is reasonably transparent.

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 extremely compact: three short sentences, front-loaded with the core purpose and key differentiator ('Unpaid probe'), then follow-up on behavior, result, and cost. Every sentence earns its place with no filler.

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 low complexity (one required parameter), the existence of an output schema to cover return details, and the description's coverage of cost, safety posture, and result categories, the definition is adequately complete. The main missing piece is explicit guidance on when to choose this tool over preview/route, but that is largely a usage-guideline concern.

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%, with the url parameter already described as an https URL of the seller endpoint to probe. The description adds no additional parameter semantics beyond restating 'seller URL'.

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 clearly identifies the tool as an unpaid probe that determines whether a seller URL is agent-ready, with a fail-closed SSRF posture. It names the specific resource (seller URL) and the type of result (readiness, claimed vs observed, flags). It does not explicitly differentiate itself from siblings preview and route, but the resource and action are distinct enough.

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 phrase 'Unpaid probe' and 'Does not charge' imply the tool is appropriate for a no-cost validation check before committing to paid or deeper operations. However, it does not explicitly state when to use validate versus preview or route, nor does it describe any exclusions or alternatives.

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