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

Annotations already declare readOnly/openWorld/idempotent, so the safety profile is covered. The description adds real behavior beyond that: it follows redirects, returns final_url, and explains favicon_source (declared vs /favicon.ico guess) — meaningful disclosure the annotations cannot express.

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, front-loaded with the core action and its outputs, then the redirect behavior, then the alternative tool. No filler.

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 helpfully names key return fields (final_url, favicon_source). It stops short of describing failure behavior (non-HTML pages, unreachable hosts) or output shape, but for a single-param read tool this is largely sufficient.

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?

Single url parameter with 100% schema description coverage, so the schema already documents it. The description adds only marginal framing (what gets extracted from that URL); baseline 3 is appropriate when the schema carries the load.

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 (fetches/extracts) and resource (web page metadata), enumerating exactly which fields are pulled (title, description, canonical URL, OG/Twitter tags, favicon). It distinguishes itself from sibling redirect_trace by naming it directly.

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?

Explicitly routes the agent to redirect_trace when per-hop redirect data is wanted, which is clear alternative guidance. It does not address other plausible neighbors (url_reputation, security_headers), but the primary competing use case is covered.

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