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

Annotations already mark this read-only, idempotent, non-destructive, and open-world, but the description adds much more: a 10-hop cap, the fact that page bodies are never read, the full list of safety flags computed, the low/medium/high risk scale, and the two-step x402 payment handshake. That payment flow is the kind of operational detail annotations cannot express and would otherwise strand the agent on a PaymentRequired response.

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 outcome, then the flags, then the when-to-use, then cost and payment mechanics — a sensible ordering with no filler sentences. The flag enumeration and the payment retry sentence are dense, but each clause conveys information an agent actually needs before calling.

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, yet the description compensates by naming every returned element (final URL, status, chain, the nine flags, risk level), and it covers the non-obvious paid-invocation protocol. For a one-parameter tool, nothing needed to call it correctly or interpret the result 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 description coverage is 100% and the single 'url' parameter already documents the example, length bounds, https:// normalization, and refusal of private/loopback hosts. The description adds no parameter-level detail beyond what the schema already provides, so the 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 ('follows a URL's HTTP redirects hop by hop') and enumerates exactly what is returned: final URL, status, full chain, and named heuristic safety flags. It is unmistakably distinct from siblings like dns_lookup, whois_domain_age, and email_auth_check, which operate on domains or mail infrastructure rather than on a single link's hop chain.

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 ('Use before an agent clicks, fetches or forwards an unfamiliar or shortened link') and an explicit exclusion ('Not a malware-reputation lookup'), so the agent knows both when to reach for it and when to look elsewhere. The cost line ($0.01 USDC) also lets the agent weigh it against free sibling lookups.

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