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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint. The description adds valuable behavioral context beyond these: per-item partial success (malformed/absent IDs land in failed[] without failing others), empty found[] semantics indicating absence in the dataset, and the recommendation to pair with coverage tool. It also mentions the data source. No contradiction with annotations; in fact, it reinforces the read-only nature by explaining non-destructive error handling.

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 comprehensive but not overly verbose. The first sentence front-loads the core purpose. It then covers batch behavior, absence semantics, and pairing guidance in clear, structured sentences. It includes a data source line at the end, which is useful but could be considered optional. Slightly longer than strictly necessary, but every sentence adds value; a strong structure with no filler.

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?

Given the tool's complexity (batch, multiple datasets, reference genomes, partial success), the description covers all necessary operational details: accepted ID formats, dataset-to-genome mapping, error handling, and absence interpretation. Since there is an output schema (presumably documenting return fields), the description doesn't need to explain return values. The inclusion of the data source and the pairing suggestion for coverage completes the picture for correct invocation.

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%, with each parameter described. The description adds substantial enrichment: it clarifies the meaning of dataset values (e.g., gnomad_r4 is GRCh38 default), provides concrete variant ID examples (1-55051215-G-GA, rs11591147), explains how reference_genome is derived from dataset and the requirement of coordinate alignment. These details go beyond the schema and help the agent construct correct calls.

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 clearly states the verb 'Fetch' and the resource 'full gnomAD population record for one or more variants', enumerating the specific data fields (allele counts, homozygote/hemizygote counts, quality flags, transcript consequence, in-silico scores, ClinVar significance). It distinguishes itself from siblings by framing the answer as 'how common, is it benign' and explicitly referencing gnomad_get_coverage for absence confirmation, which sets it apart clearly.

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 provides explicit usage context: 'The ''how common, is it benign'' answer in one call.' It also gives a clear pairing instruction with gnomad_get_coverage for confirming absence, and explains the batch behavior with per-item partial success and failure handling. This effectively tells the agent when to use this tool versus alternatives, including a direct reference to a sibling tool.

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