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

Annotations already mark the tool read-only, idempotent, and open-world, so the description only needs to add behavior beyond those. It adds source aggregation (50K+ publisher/repository sources), describes the returned oa_status values, and clarifies auth: no user credential, only an internal contact email per API terms. It does not contradict annotations.

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?

Four sentences, each carrying distinct information: what it does, what it returns, how it differs from siblings, and auth/data source. The main action is front-loaded. It is dense but not verbose, with every sentence earning 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?

For a one-parameter read-only lookup with an output schema and safety annotations, the description covers purpose, response content, auth, source, and sibling alternatives. An agent has everything needed to decide and invoke correctly. No material gap remains.

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 only parameter, doi, is 100% covered by the schema, which specifies type, minLength, requirement, and format examples. The description only repeats 'by DOI' and adds no semantic detail beyond the schema. Baseline 3 applies because the schema carries the semantic burden.

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?

Description opens with a specific action and target: 'Look up the open-access status of a scholarly work by DOI' and promises a direct link to full-text. It names concrete return fields and explicitly separates itself from education.doi_lookup and crossref.works_search, which return bibliographic metadata. This clearly distinguishes it from sibling research-API tools.

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 sentence 'Complements education.doi_lookup and crossref.works_search (which return bibliographic metadata, not full-text availability)' tells the agent that this tool is appropriate when OA status or full-text availability is the goal. It also implies the alternatives when bibliographic metadata is needed. It lacks an explicit 'use X instead' construction, but the contrast is clear routing guidance.

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