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

With no annotations, the description carries the full burden, and it delivers the single most operationally important fact: this is a paid tool with three settlement paths (0.01 USDC on Base via x402, 12 sats Cashu NUT-24, 12 sats Lightning L402). That is the equivalent of an auth/cost requirement an agent must budget for. It still omits failure modes (unreachable URL, non-redirecting URL) and any rate limits.

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, front-loaded with the purpose and the output shape before the cost detail. The payment sentence packs three options into one line, which is slightly dense but every clause is operationally relevant.

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 one-parameter paid utility with no annotations and no output schema, the description is adequate but incomplete: it outlines the return content in prose yet omits error behavior for non-shortened or unreachable URLs, and gives no hint about how the payment step is triggered or confirmed before the call succeeds.

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?

The schema has one required parameter with 0% description coverage, so the description must compensate and largely does not. It implies the input is a shortened/redirecting URL, but adds nothing about format (scheme required?), validation, or what happens with a URL that does not redirect.

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 verb 'Expands' plus the resource 'a short or redirecting URL' is specific, and the description even previews the output (full redirect chain, status codes, final destination). It does not explicitly position itself against any sibling, but among the mostly unrelated siblings (dns_lookup, links, headers) its role is unambiguous.

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?

Usage is implied rather than stated: an agent can infer it should call this when it holds a shortened or redirect-wrapped URL. There is no explicit when-not-to-use, no mention of an alternative tool (e.g. links or headers), and no prerequisites such as requiring a funded wallet.

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