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

Goes well past the readOnlyHint annotation: it discloses that fetching is server-side and SSRF-hardened with private ranges blocked, HTTPS-only, and per-hop validation, and it enumerates the per-hop artifacts returned (status, IP, TLS, timing) plus phishing flags. This is unusually rich behavioral context for a read-only tool.

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 core action in the first clause, followed by output contents and safety notes. The parenthetical lists are dense but every item carries information; only marginal trimming is possible.

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 no output schema, the description compensates by enumerating the returned fields, and it covers the safety profile and the SSRF posture. For a single-parameter read tool, an agent has everything needed to call it 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 only one parameter and schema description coverage is 100%, so the schema already documents the url field. The description adds the notion that a URL is resolved server-side but no format or syntax detail beyond the schema. 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 precise verb and resource: 'Follow a URL server-side through every HTTP redirect hop to its real final destination'. The scope is unmistakable and cannot be confused with siblings like whois_lookup or analyze_eml, which operate on different inputs.

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 phishing/deliverability framing implies when the tool is useful, but there is no explicit statement of when to use it versus an alternative, nor any prerequisites or exclusions. Usage must be inferred from the described output rather than stated.

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