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

Annotations already declare readOnly/idempotent/openWorld, and the description adds substantive traits beyond them: 1-request-per-3-second pacing, caching behavior, the $0.001/call price with 10 free/day and x402 payment fallback, and error semantics (isError on invalid input/upstream failure, not charged). This is exactly the extra context an agent needs before calling.

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?

Purpose is front-loaded in the first clause, and each subsequent sentence covers a distinct concern (query syntax, pacing/caching, pricing, errors) with no filler. Dense but every sentence 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?

An output schema exists so return values need not be re-explained, and the description still sketches the payload (abstracts, authors, dates, PDF links). Pricing, rate limits, caching, and error behavior are all covered, leaving no material gap for correct invocation.

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. The description adds arXiv query-syntax semantics beyond the schema's examples (ti:, au:, abs:, cat:cs.AI, AND/OR), clarifying what the required 'query' string actually accepts. Sort and limit are already fully documented in the schema.

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 and resource ('Search arXiv research papers') plus scope (keywords, author, category) and sort modes. It is clearly distinguishable from siblings like book_search, hn_search, wiki, and doi_lookup without opening any 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?

Gives clear context for when this tool applies (arXiv academic literature) and notes the two sort intents, but never names an alternative or a when-not condition (e.g. vs. doi_lookup for DOI resolution or web_read for arbitrary pages). Clear context, no explicit exclusions.

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