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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does add value by stating the idempotency_key requirement (including the header alternative) and the two possible return types. However, it does not explain what conditions lead to ActiveLinkCreated versus NonActiveLinkCreated, nor does it disclose side effects, rate limits, or permission needs. It is more informative than a tautology but lacks depth for a mutation tool.

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?

The description is only two sentences and front-loads the core purpose. There is no fluff, and the idempotency requirement is mentioned right after the return types. It is slightly lacking in structure—no use of bullets or clear separation of concerns—but it is appropriately sized for the tool.

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 tool with 7 parameters and no annotations, the description is under-specified. It does not clarify the distinction between url and longUrl, nor alias and customSlug, which could lead an agent to misuse them. It also does not explain the business meaning of the two return types or any error handling. The output schema exists, but the description's mention of it is not enough to cover the full context an agent needs to call this tool 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?

Schema coverage is 71%, so the description does not need to repeat parameter details. It does add one semantic nuance: idempotency_key can be passed as an argument or via the Idempotency-Key header, which is not fully captured in the schema description. However, it adds nothing about url vs longUrl or alias vs customSlug, which are potentially confusing duplicates. Given the high schema coverage, a baseline of 3 is appropriate, with the idempotency clarification being a minor bonus.

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 clearly states the action ('Create a single short link'), names the HTTP endpoint, and the word 'single' distinguishes it from the sibling shorten_urls (plural). It also mentions the return types, which further clarifies its scope. This is a specific verb+resource statement that an agent can easily act on.

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?

There is no explicit guidance on when to use this tool versus alternatives. It only says 'single', which implicitly contrasts with the plural shorten_urls, but it does not name the sibling or state conditions for choosing one over the other. It also does not mention any exclusions or prerequisites beyond the idempotency_key requirement.

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