xguard.preflightFree, read-only safety gate for xguard.web.fetch. Validates the public HTTPS target, SSRF policy, DNS reachability and selected payment path without contacting the target or attempting payment. On allow, call xguard.web.fetch directly; it creates the signed quote and returns the mandatory x402 v2 PaymentRequired result.
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the annotations (readOnlyHint, idempotentHint, openWorldHint), the description discloses the side-effect profile that matters: it is free, does not contact the target, and does not attempt payment, despite performing DNS reachability checks. It also explains the downstream behavior of xguard.web.fetch, which creates the signed quote and returns the mandatory x402 v2 PaymentRequired result.
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 tight sentences with no filler, front-loading the identity of the tool and then the validation scope and routing rule. The final clause about the x402 v2 PaymentRequired result is useful but slightly dense; overall it is efficient and well ordered.
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 sprawling multi-envelope input schema and the absence of an output schema, the description covers the essential gate semantics and the hand-off to fetch. It leaves the failure/deny path and the contents of a preflight success result implicit, which is a modest gap for a tool whose main value is a pass/fail verdict.
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 enumerates the accepted envelopes plus x-xguard-accepted-shapes examples, so the schema carries the parameter semantics. The description adds no parameter-level meaning such as which fields drive the payment-path selection or how network/testnet affect the check, so the baseline 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 gives a specific verb and resource: a 'read-only safety gate for xguard.web.fetch' that validates the HTTPS target, SSRF policy, DNS reachability and payment path. It explicitly names the sibling it guards, so an agent can distinguish it from xguard.web.fetch, xguard.capabilities and xguard.pricing.quote 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?
It states the workflow rule 'On allow, call xguard.web.fetch directly', which tells the agent this tool precedes fetch and is not itself the fetch. However, it never says what to do when the preflight denies, nor whether preflight is mandatory or optional before every fetch, so the guidance is clear but not exhaustive.
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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