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

With no annotations, the description carries the full burden and does well: it discloses the paid x402 flow, the price and network, browser-like probing, and precisely what the blocked flag means (401/403/429/503 only). It omits rate limits, retry/redirect behavior, and what happens on timeouts or DNS failures.

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 tight sentences covering cost, purpose, outputs and the cheaper-than-fetch rationale, with no filler. Leading with the pricing bracket is slightly unusual ordering, but it is information an agent needs before committing to a paid call.

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?

There is no output schema, and the description compensates by listing every returned field, including the conditional blocked flag. Cost, network and the core usage condition are all present, so an agent has enough to decide and invoke 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?

There is a single parameter at 100% schema coverage, so the schema already defines it as a full http(s) URL. The description adds only the framing that the URL is probed as a browser, which affects interpretation but is not parameter-level detail. Baseline 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?

States a specific verb and resource ('Reachability check of a URL as a browser') and enumerates the exact outputs (status code, latency, server header, content type, size, blocked flag). It also draws the line against a fuller fetch, which separates it from the crowded web_* and site_audit_* siblings.

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 decision rule: use this when an agent only needs to know if a source is alive, because it is cheaper than a full fetch. It stops short of naming the sibling to use instead (web_fetch) or stating exclusions such as when a body/rendered DOM is required.

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