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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds meaningful behavioral context: the 15-hop limit and the specific return data (each hop's status code and domain-crossing flag). It doesn't mention network side effects, but for a read-only tool that's acceptable. No contradictions.

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 sentences with no wasted words. The first sentence front-loads the core functionality and constraints (15 hops, status codes, domain crossing), and the second gives a practical use case plus a pointer to a sibling tool. Efficient and well-structured.

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?

Given there is no output schema, the description adequately describes what the tool returns (every hop with status code and domain-crossing flag). It also mentions the hop limit and a use case. It doesn't detail error handling or the exact response structure, but for a one-parameter read-only tool, this is sufficient. A 4 is fair because it covers the essentials without being exhaustive.

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% — the URL parameter is fully described ('URL to follow the full redirect chain for, hop by hop'). The description adds the hop limit and output details, but these are behavioral facts, not parameter semantics. Since the schema already documents the only parameter, the description doesn't need to compensate, and a baseline 3 is appropriate.

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?

The description states a precise action ('follows a URL's full redirect chain') with a clear resource (URL) and limits (up to 15 hops). It also distinguishes itself from siblings like url_reputation and url_clean by explicitly mentioning the output (each hop's status code and domain crossing) and its intended use case (seeing where short or tracking links lead).

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?

It provides a concrete use case ('use it to see where a short or tracking link really leads') and a complementary follow-up ('check the final URL with url_reputation'), which implies when this tool is appropriate versus alternatives. However, it doesn't explicitly state when not to use it or name direct alternatives beyond the reputation check, so it misses some exclusionary guidance.

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