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 genuinely useful context beyond that — free daily allowance, then $0.05 USDC via x402 or 3 credits with X-API-KEY — which an agent needs for cost/rate awareness. It does not disclose what the snapshot contains or how many calls consume allowance.

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 compact fragments with the core purpose front-loaded and zero filler. The pricing parenthetical is dense but earns its place as cost information; nothing is redundant.

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?

For a one-parameter read-only tool with no output schema, the definition covers purpose, cardinality limits, and billing. The only remaining gap is which attributes the comparison returns, which is a minor omission for a snapshot tool.

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 parameter (comma-separated slugs) is already documented. The description adds a real constraint the schema omits: the count must be 2-5 peptides, which the schema does not enforce or state.

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?

"Side-by-side snapshot of 2-5 peptides" states the resource (peptides) and the operation (comparison snapshot), which distinguishes it from single-record siblings like get_peptide or get_dossier. It never names an alternative explicitly, so sibling differentiation is implied rather than stated.

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?

There is no guidance on when to use this versus get_peptide, get_peptide_summary, or get_dossier for multi-peptide questions. The only conditional content is the billing note (free allowance, then paid), which tells the agent about cost, not about tool selection.

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