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

Beyond the readOnly and openWorld annotations, the description discloses auth requirements (contact e-mail, no key), the return limitation (metadata and links only, not the PDF), and a precise cost/payment model including that failed calls are not charged. These are high-value behavioral details an agent cannot infer from structured fields.

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 front-loaded with the core purpose and then layers in auth, output scope, and pricing. Every sentence carries useful information for invoking the tool correctly, with no wasted filler.

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?

Given a simple one-parameter schema, full schema coverage, an output schema, and existing annotations, the description fills the remaining gaps: environment prerequisite, output limitation, and per-call cost. Nothing an agent needs to call this tool correctly is missing.

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%, and the sole parameter is already documented with an example DOI in the schema. The description reinforces that lookup is by DOI but does not add syntax, format, or edge-case semantics beyond what the schema provides.

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 states a specific verb and resource: an Unpaywall open-access lookup by DOI. It names the exact outputs (OA status, best free full-text link, journal, publisher), which distinguishes it from generic academic search siblings like search_crossref or search_pubmed_article_metadata.

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?

Usage is clear from the DOI-based lookup framing and the prerequisite that UNPAYWALL_EMAIL must be set. It does not explicitly name alternative tools or when-not-to-use conditions, but the context is sufficiently clear for an agent to select it for OA checks.

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