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

Goes well beyond the readOnlyHint/openWorldHint annotations by disclosing the payment model (x402, USDC, Base/Solana/Arc), the exact price per successful call, and that failed calls are free — critical cost behavior for an agent deciding whether to invoke. Also discloses an output limitation (scope notes absent) that annotations cannot convey.

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?

Three dense, front-loaded sentences: what it returns, the exact-match limitation, then cost. No filler, and the most decision-relevant constraint (exact match) precedes the pricing detail.

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-shape gaps are covered, and the description still names the returned fields. Payment, failure-charging, and the exact-match requirement give an agent everything needed to call it correctly without probing.

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% and the single 'heading' parameter is fully documented with charset and length constraints, so the schema carries the parameter burden. The description only reinforces the exact-match requirement, which is useful but adds little beyond the schema baseline.

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?

Names a specific source (NLM MeSH), a specific resource (one descriptor for an exact heading), and enumerates exactly what is returned (ID, label, entry terms, allowable qualifiers). No sibling tool covers MeSH, and the scope is unambiguous from the first clause.

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?

Explicitly states the operative constraint ('Exact match only') and one exclusion ('no scope notes, the public lookup API does not return them'), so an agent knows a partial/fuzzy heading will fail. It stops short of suggesting an alternative for non-exact lookups, which keeps it below a 5.

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