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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so the safety profile is covered. The description adds the external authorities queried (Ensembl, MyGene, UCSC, GTEx, BioMart), aligning with openWorldHint, but discloses no auth needs, rate limits, or side effects; 3 reflects adequate but minimal added context.

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 no filler. The list of data sources is dense but directly relevant, so the description is appropriately sized.

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 an output schema and full parameter descriptions available, the description need not explain returns or each parameter. It gives a clear purpose and data sources, but omits any routing against the many sibling lookup tools, leaving a small contextual 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%, so the baseline is 3. The description loosely maps to the source enum by naming the five authorities, but adds no syntax, format, or command guidance beyond what the schema already provides for query, source, limit, _subject, and _files.

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?

Specific verb 'look up' and resource 'gene or genomic region', then enumerates the record types (Ensembl, cross-references, MyGene, UCSC, GTEx, BioMart). It distinguishes itself from protein/variant/clinical lookup siblings by resource, but does not explicitly name an alternative or scope boundary, so 4 rather than 5.

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?

No when-to-use, when-not, or alternative-tool guidance is given. The list of sources implies that source selects the authority, but that is schema/enum semantics rather than usage routing, and no condition tells an agent to choose lookup_gene over lookup_variant or browse_region.

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