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

Adds substantial context beyond annotations: 10-hop cap, loop detection, SSRF protection ('every hop is checked before it is requested; redirects to private addresses are reported, not followed'), page not loaded, and per-call pricing with repeats not free. These details matter because idempotentHint=false is otherwise unexplained.

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?

Purpose and safety behavior are front-loaded, use cases and an example follow, and pricing is last. Slightly heavy on billing detail ('x402 USDC or a card key (/credits)') for a tool description, but nothing is buried or 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, and the description fully specifies the return shape: every hop's status code and Location, final URL, total hops, timing, loop flag. Combined with the hop limit and private-address handling, an agent has everything needed to call it and interpret results.

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% for the single url parameter ('Absolute http(s) URL'), so the schema already carries the semantics. The description only adds an example (url=http://github.com) and no format or edge-case guidance beyond what the schema states.

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: 'Follow a URL's redirects hop by hop ... return every hop's status code and Location' and explicitly covers short-link expansion. An agent can distinguish it from sibling url_meta (metadata), url_uptime (availability), and extract (page content) 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 concrete use cases: unshorten a link, check an HTTPS or www redirect, debug SEO redirect chains. It does not name a sibling alternative or an explicit when-not-to-use condition, which keeps it below a 5.

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