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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds meaningful behavioral context: it applies two specific published rule sets, computes over each side's full typing QC, and explicitly states it is decision support only and not a medical device. This goes beyond the annotations and clarifies the tool's limitations.

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?

The description is compact and front-loaded with the core purpose, then details the rule sets, then the input format, then the safety disclaimer. Every sentence earns its place, though the input format sentence is slightly redundant with the schema's parameter descriptions. Still, it's efficient and well-ordered.

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?

The tool has an output schema, so return values need not be explained. The description covers the rule sets, input constraints, and safety limitations. It doesn't mention edge cases like what happens with missing loci or multiple mismatches, but for a read-only decision-support tool with a rich schema and output schema, the description is largely complete.

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%, so the schema already documents both parameters thoroughly, including the 'allele strings only' privacy constraint. The description reinforces the privacy constraint and the structure (locus -> allele arrays), but doesn't add new parameter-level meaning beyond what the schema provides. Baseline 3 is correct.

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?

The description names a specific verb ('compatibility under two published rule sets'), a precise resource (HLA-B leader match and KIR ligand class comparison), and explicitly distinguishes itself from ranking/recommendation tools. It also names the sibling it is not ('does not rank or recommend a donor'), which separates it from match_score.

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 description states what it computes and explicitly says it does not rank or recommend, which implies when not to use it. It does not explicitly name alternatives like match_score or check_typing, but the 'does not rank or recommend' exclusion gives clear usage boundaries. A 4 is appropriate because the context is clear but no explicit alternative tool is named.

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