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

Annotations already declare readOnlyHint=true and openWorldHint=true, but the description adds real behavioral context beyond them: the record's field coverage, a hard cap of 10 frequency rows per call, and an explicit pricing model ($0.002 USDC per successful call via x402 on Base/Solana/Arc, failures not charged). That cost-and-limit disclosure is exactly the kind of detail the annotation cannot carry; only error/empty-result behavior is absent.

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?

Two sentences, front-loaded with the verb and resource, then a compact field list, a row limit, and pricing. The parenthetical '(e.g. 1000 Genomes allele counts)' and the payment-rail enumeration are slightly dense but each clause carries information an agent would otherwise have to discover by trial.

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-value explanation is optional, and the description still summarizes the payload plus the 10-row frequency cap and the billing rule. For a one-parameter read-only lookup this is close to complete; the only gaps are sibling routing and failure behavior.

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?

There is a single required parameter with 100% schema description coverage ('dbSNP rs number, e.g. rs429358'), so the schema already does the work. The description's mention of 'by rs number' restates rather than augments the schema; no format rules, versioning notes, or invalid-ID handling are added.

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/resource pair — retrieve an NCBI dbSNP short variant record by rs number — and enumerates exactly which fields come back (variant type, placement, ref/alt sequence, allele frequencies). That is enough for an agent to distinguish it from siblings like health_clinvar_genetic_variants or health_genbank_nucleotide_seq, though the description never names those alternatives explicitly.

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?

Usage is only implied: an agent infers this is the tool for rs-number variant lookups. There is no statement of when to prefer it over ClinVar, GWAS Catalog, or GenBank siblings, and no note about prerequisites such as needing a valid rsID or the fact that only short variants (not structural variants) are covered.

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