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

readOnlyHint=true already tells the agent this is a safe read. Beyond that the description adds only an API route reference, saying nothing about not-found behavior, whether any of the four optional identifiers must be supplied, or rate limits. No annotation contradiction, but virtually no added behavioral context.

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?

One front-loaded sentence with the identifier options first and the route reference last. Zero filler; every clause carries information.

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?

With zero required parameters, an agent needs to know the valid identifier combinations, and the description supplies them. No output schema exists, though the description would ideally note the not-found case given four all-optional parameters.

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 100%, so the baseline is 3, but the description adds genuine meaning the schema does not: it frames linkId, externalId, and the domain+key pair as alternative lookup strategies, not just four independent fields. It stops short of stating that only one strategy should be used per call.

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 (fetch) and resource (a single link), and enumerates the three accepted identifier schemes. The word 'single' plus the named key combinations cleanly separate it from dub_list_links and dub_count_links.

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 three lookup modes imply 'use this when you already have an identifier', which is useful, but the description never says when to prefer this over dub_list_links or what to do when the link does not exist. Usage is left implicit rather than stated.

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