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

Annotations already cover safety (readOnlyHint, idempotentHint, openWorldHint=false), so the description's job is to add beyond that — and it does: deterministic sort order, an explicit tie-break rule (non-affiliate first), and the exact fields each entry carries. It does not mention result size, pagination, or freshness of COA data, which keeps it from a 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?

Three short sentences, front-loaded with the scope and ordering, then the tie-break, then the returned fields. No filler and every clause conveys actionable information.

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 parameters and no output schema, the description carries the return-shape burden and does enumerate the fields (grade + band, COA status, buy link, coupon, is_affiliate). It stops short of saying how many vendors or whether results are complete/truncated, a minor gap for a simple read-only list 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The mention of sorting and tie-break describes output ordering rather than input semantics, which is correctly out of scope here.

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 resource and scope: 'Every PepEvolution-graded research-peptide vendor', plus the ordering (PepScore desc) and tie-break. An agent can tell this is the full enumeration tool rather than a single-record lookup like check_vendor or a lookup like find_peptide_sources, though no sibling is named 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 by the 'Every ... vendor' framing — use it when you want the whole graded list. There is no explicit when-to-use guidance, no statement of when to prefer check_vendor or find_peptide_sources instead, and no prerequisites or exclusions.

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