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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=true). The description adds genuinely new behavioral context: it returns destination URL and domain plus a redirect count, and that the full redirect chain is gated behind paid plans. The 10-credit cost disclosure is real value beyond the annotations. Return shape details are left to the output schema, which exists.

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 compact sentences, front-loaded with the core purpose followed by the output and tier/cost note. Minor redundancy in restating the tool name and title at the start, but nothing wasteful.

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?

Output schema covers return values, annotations cover safety, and the description adds cost and plan-tier constraints. The only real gap is error behavior for non-short or already-resolved URLs, which is a modest omission for a single-parameter read tool.

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 with 100% schema description coverage ('The shortened URL to unshorten') plus an example. The description adds no syntax, validation, or edge-case meaning (e.g., what happens if the input is not a short link, or if it is already unshortened). Baseline 3 applies when the schema carries the semantics.

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: 'expands shortened links to reveal their final destination URL and destination domain.' That is concrete enough to separate it from generic URL tools like URLLookup or URLTitle, though it never names those siblings explicitly.

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?

'Send any short link to inspect the resolved address' implies the input condition but gives no when-not guidance and no named alternative for related tasks (e.g., URLTitle for page titles, URLLookup for general URL metadata). Usage is inferable rather than directed.

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