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

With no annotations provided, the description must fully disclose behavioral traits. It states that the tool checks open-access status and provides a PDF link, but it does not mention whether the operation is read-only, if authentication is required, if there are rate limits, or how invalid DOIs are handled. The behavioral transparency is minimal and insufficient for a tool with no annotation safety net.

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 extremely concise and front-loaded, with no redundant words. It conveys the core function in two short phrases. However, its brevity sacrifices necessary context, such as input semantics and usage guidelines, making it efficient but potentially too terse for reliable tool selection.

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?

Even though an output schema exists, the description is incomplete for a one-parameter tool. It fails to clarify what 'q' should contain, does not provide usage context or alternatives, and omits behavioral details that would normally be covered by annotations. An agent would likely need additional inference 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?

The schema has a single parameter 'q' with a default of '' and no description, and schema coverage is 0%. The description does not explicitly state that 'q' is the DOI, though it is implied by the tool's purpose. Since the schema provides no explanation, the description should clarify the expected input format and value, but it does not, leaving the agent to guess.

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 tool's purpose: checking if a DOI is open-access and providing a direct PDF link. This distinguishes it from siblings like 'doi' (likely metadata resolution) and 'crossref' (bibliographic metadata). However, it is phrased as a question rather than an explicit action, and the resource (DOI) is implied rather than stated, so it's not perfect.

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 guidance on when to use this tool versus alternatives such as 'doi', 'crossref', or 'openalexwork'. The description does not mention any prerequisites, exclusions, or specific conditions for choosing Unpaywall over other DOI-related tools. This leaves the agent to infer usage from the name and description alone.

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