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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so the safety profile is covered. The description adds genuine behavioral value by disclosing that it follows 'every hop of the redirect chain' to the final destination, which tells the agent what output semantics to expect.

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 and appropriately short, but the opening three fragments ('Expand a shortened link. Expand short URL. Expand short links...') restate the same idea redundantly before reaching the informative content about redirect chains.

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?

For a single-parameter read-only tool with no output schema, the description covers what it does, the range of inputs accepted, and the redirect-chain behavior. It could say more about the return shape (final URL plus hop list), but an agent has enough to invoke 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?

Only one parameter (url) with 100% schema description coverage, so the schema already documents it. The description's shortener examples add mild context but no syntax or format detail beyond the schema's own example. 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+resource (expand a shortened link) and goes further by naming example shorteners (bit.ly, t.co, tinyurl) and clarifying it handles 'any redirect'. This distinguishes it from siblings like link_preview or check_url_status, which an agent might otherwise confuse it with.

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 closing line 'Check where a link really goes before clicking it' implies the use case, but no sibling is named and there are no explicit when-not conditions (e.g., when to prefer check_url_status or link_preview). Usage is implied rather than specified.

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