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

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds valuable context: it is 'Keyless' (no auth needed), returns the same full record as get_gene (clarifies output format without needing an output schema), and the term 'Reverse-lookup' sets clear behavioral expectations. No contradiction with annotations.

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 extremely concise: one sentence for purpose, a brief example, a list of accepted IDs, and the keyless note. Every sentence adds value. It is front-loaded with the core action ('Reverse-lookup'). No wasted words.

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 simplicity (2 parameters, no nested objects, no output schema), the description covers input types, the mapping concept, output shape (same as get_gene), and authentication (keyless). It does not detail the output structure, but referencing get_gene leverages existing knowledge. Slightly incomplete for agents unfamiliar with get_gene, but adequate overall.

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 descriptions for both parameters. The description adds concrete examples (e.g., Entrez '672', Ensembl 'ENSG00000012048') but does not explain the meaning beyond what the schema already provides. It reinforces that the ID is external, which is helpful but not essential. Baseline 3 is appropriate.

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 tool's function: 'Reverse-lookup: map an external database id to its canonical HGNC gene.' It provides a concrete example ('What gene is Entrez 672?' -> BRCA1) and lists all supported ID types. It distinguishes itself from sibling 'get_gene' by noting it returns the same record, implying get_gene uses canonical symbols instead.

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 specifies when to use the tool (when you have an external ID and need the HGNC gene) and lists all accepted ID types. It mentions 'Keyless' indicating no authentication overhead. However, it does not explicitly state when not to use it or name alternative tools, though the sibling list and mention of get_gene provide implicit guidance.

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