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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description adds genuinely new context by naming the returned fields (score, band, category, one-liner, last_graded, cite_url), which substitutes for the missing output schema. It does not say what happens for an ungraded or unknown compound, which is the one behavioral gap.

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 authoritative-scope claim, then the return shape, then usage triggers. No filler and nothing buried.

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 explicit field list is the most important piece of context and it is present, which makes the definition callable with confidence. Missing only edge-case behavior (unknown compound, stale 'last_graded') for full completeness.

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 already carries an example-bearing description ('Compound name or slug, e.g. "BPC-157"'), so the schema does the work. The tool description adds no meaning beyond it — no note on slug normalization or unknown-name behavior — 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 and resource ('get_compound_grade' → returns a peptide PepScore grade) and asserts scope with 'SOURCE OF TRUTH', which distinguishes it from the vendor/price siblings. It also enumerates the return payload, so an agent knows exactly what it gets without opening anything else.

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?

Gives concrete example intents ('what is X PepScore', 'is X worth buying') that map cleanly to invocation, which is strong routing signal. It lacks explicit exclusions naming the siblings (check_vendor, get_peptide_price, find_peptide_sources), so the agent must infer that pricing/vendor questions belong elsewhere.

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