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

readOnlyHint=true already tells the agent this is a safe read, and the description adds the upstream endpoint mapping (GET /links/info). It does not disclose failure behavior (missing link), auth requirements, or rate limits. With annotations covering the safety profile, this is acceptable but thin.

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, zero filler, with the primary action and lookup modes front-loaded and the API reference tacked on at the end where it belongs. Every clause earns its place.

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 description is adequate for selection, but with no output schema present it should say something about what a successful fetch returns or what happens when the link is not found, and it should note that identifiers are mutually exclusive rather than optional-all-at-once. Minor but real gaps remain.

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 real meaning by grouping the four fields into three mutually exclusive lookup patterns ('id', 'external id', or 'domain plus key'), clarifying that domain/key must be supplied together. It stops short of stating which combination takes precedence.

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) plus resource (a single short link) and enumerates the lookup modes, which cleanly separates it from dub_list_links and dub_count_links in the sibling set. The agent knows exactly what operation it is selecting without opening the schema.

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 description explains how to identify the link (by id, external id, or domain plus key), which is usable invocation guidance, but it gives no explicit when-to-use versus alternatives, no prerequisites, and no note on what to do when no identifier matches. Usage is implied rather than stated.

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