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

Annotations cover readOnlyHint and openWorldHint, and the description adds genuinely non-obvious behavior: a free daily allowance followed by metered cost ($0.02 USDC via x402 or 1 credit with X-API-KEY). That pricing/quota disclosure is real value an agent cannot get from annotations. It doesn't mention rate limits or what a lookup miss returns, keeping it below 5.

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 tight sentence for purpose plus a parenthetical for billing; front-loaded and no filler. Minor deduction because the two concerns are jammed into a single sentence rather than separated.

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?

A read-only single-param lookup is a simple case, and the billing detail is a helpful addition, but with no output schema the description should say more about what the snapshot returns (depth, format) and what happens for unknown slugs or when the free allowance is exhausted.

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 param ('slug' or alias) is already described in the schema. The description adds nothing about slug formatting or alias resolution beyond that, so 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 (implicit fetch) and resource (peptide snapshot) and enumerates the returned sections: identifiers, mechanism, indications, at-a-glance. It distinguishes itself from siblings like get_identifiers or get_peptide_summary by being the composite 'full snapshot', though it doesn't explicitly say so.

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?

The word 'Full' combined with sibling names such as get_peptide_summary and get_identifiers implies this is the broad composite call, but there is no explicit when-to-use/when-not guidance or named alternative for narrower needs.

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