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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the description's credit comes from added context: a per-call cap of 5 concepts, per-call pricing ($0.002 USDC via x402, Base/Solana/Arc), and the fact that failed calls are not charged. That payment/limit detail is exactly the kind of behavior an agent needs before invoking a paid external lookup; only the response shape is left to the output schema.

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?

Front-loaded with the verb and resource, then constraints, then price. Every clause carries information (term-type examples, exact-match constraint, pricing terms), though the payment detail is a touch verbose for a single sentence.

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 needn't be spelled out, and the annotation pair covers safety. The description supplies the missing operational context (cap, pricing, exact-match behavior). Only a pointer to an alternative for non-exact lookups is absent.

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%, with both `name` (allowed characters, 2-100 chars) and `max` (1-5, default 3) documented. The description reinforces the cap with "Up to 5 concepts per call" but adds no syntax or semantics beyond the schema, so the baseline 3 applies.

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 (NIH RxNorm concept lookup via RxNav) and the exact return content (RxCUI identifiers plus each concept's name and term type, with IN/SCD examples). This clearly separates it from siblings like health_drugbank_interaction or health_daily_med_label_spl, which serve different drug-data purposes.

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?

"Exact-name lookup, no fuzzy matching" gives a real when-not condition, telling the agent this tool fails on partial or misspelled names. It does not name a sibling alternative for fuzzy/ID-based lookup, so routing guidance is clear but incomplete.

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