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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds meaningful context beyond that: a free daily allowance, then per-call pricing ($0.02 USDC via x402 or 1 credit with X-API-KEY), and that the UNII value is cross-checked against openFDA — all genuine behavioral/auth/cost disclosure.

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?

One compact sentence with the returned-field list front-loaded and pricing moved to a parenthetical. Dense but every element earns its place; the identifier list is long but informative rather than padded.

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?

With no output schema, the description usefully enumerates what comes back (UNII, CAS, PubChem CID, InChIKey, formula, ChEMBL ID, INN, ATC codes, source URLs). The main gap is that it never states the input is a peptide slug or what happens when an identifier is unavailable.

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?

Only one parameter (slug) and schema description coverage is 100%, so the schema already documents it. The description never mentions the slug or explains what a valid peptide slug looks like, so it adds nothing beyond the schema. 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?

The phrase 'Identifier crosswalk' plus an enumeration of identifier types makes clear what data is returned, but there is no explicit verb ('returns', 'looks up') and no statement of the input scope (a peptide slug). An agent can infer this returns cross-referenced identifiers for a peptide, but it must read the schema to know what it operates on.

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?

No guidance on when to use this instead of siblings like get_peptide, get_dossier, or get_regulatory, and no exclusions or prerequisites stated. The only context is the pricing/allowance note, which is about cost, not selection.

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