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

With no annotations, the description carries the full burden. It does disclose the return values ('Returns the short URL and a stats URL'), which is useful behavioral context. However, it omits any mention of authentication requirements, rate limits, permanence of links, or error behavior, leaving significant gaps.

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?

Three short sentences that are front-loaded with the core purpose and contain no filler. The optional slug sentence is somewhat redundant with the schema but does not detract from the efficient structure.

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?

The tool is simple and the input schema is rich, and the description covers the return values despite no output schema. However, without annotations it should have provided more behavioral context (e.g., authentication, link permanence) to be fully complete for an agent.

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 description coverage is 100%, so the schema already fully documents the url and slug parameters. The description's mention of an optional custom slug adds no meaning beyond what the schema provides, so the 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?

States a specific verb and resource ('Shorten a long URL') and names the output domain ('b59.link'), making it distinct from siblings like lookup_url or get_stats_url. However, it does not explicitly contrast itself with those siblings, so it falls short of a 5.

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?

Offers no explicit when-to-use guidance or alternatives. The intended use case is implied by the purpose, but nothing tells the agent when to choose this tool over lookup_url or generate_qr. This matches the calibration's 2 for a tool with no usage context.

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