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

Annotations already declare readOnly, idempotent, non-destructive and open-world behavior, so safety is covered. The description earns credit by expanding what "in full" returns — title, controlled biome classification, ENA project/study accessions, downloads, last-update date — which is genuine context beyond structured data. It stops short of noting auth or rate-limit behavior.

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?

Two sentences, zero filler. The verb+resource+scope lands first, then the return payload, then usage routing — properly front-loaded.

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 no output schema, the description carries the burden of describing returns and does so by listing the major fields. Usage routing and the single required parameter are covered. Dense studies could return more nested detail than the enumeration suggests, but nothing essential is missing 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% and the schema already documents the single accession parameter with an example. The description's "by its accession (MGYS…)" only restates the MGYS prefix format, adding little beyond the schema. Baseline 3 is appropriate here.

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 ("Fetch"), a specific resource ("one MGnify metagenomics study"), and the scoping key ("by its accession (MGYS…)"), then enumerates the returned fields. It is clearly distinguishable from mgnify_search_studies and mgnify_biomes without opening any schema.

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?

Gives two concrete triggering conditions: after mgnify_search_studies, or when a paper cites an MGYS accession. It names the sibling tool that produces the predecessor step, so the agent knows exactly where this fits in a workflow.

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