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

Annotations already establish this as a safe, non-destructive, closed-world read-only computation, so the bar is lower. The description earns credit by disclosing the computation model: it multiplies average residue mass and adds peptide bond count, which explains why results are 'Estimate'-level approximations rather than exact masses.

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?

A single front-loaded sentence with the resource and units leading. The trailing 'plus peptide bond count' clause is efficient but ambiguous about whether it is an input or a derived output, a small structural cost.

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 two-parameter pure calculator with full schema coverage and safe annotations, the definition is nearly sufficient; it even names the output units and the extra peptide-bond quantity. With no output schema, the exact response field names and numeric rounding are left unspecified, which is the only real gap.

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 description coverage is 100% with clear per-field descriptions (residue count range 1-100000, average mass in Da with an example), so the schema does the heavy lifting. The description restates the two inputs but adds no format or unit nuance beyond them, and its mention of 'peptide bond count' is an output, not an input, which risks mild confusion about arity.

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 (Estimate), resource (protein chain molecular weight), units (Da and kDa), and the exact inputs it derives from. The sibling list is entirely unrelated finance/geometry/health calculators, so no differentiation is needed, and an agent can tell instantly what this computes.

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 implied: the input description ('from residue count and average residue mass') tells the agent when the tool is applicable, i.e. when those two quantities are known. There is no explicit when-not guidance or named alternative, but no plausible alternative exists in the sibling set for most cases (e.g. avgResidueMass='monoisotopic or average?' is not addressed).

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