list_repositories

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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds the useful edge case that a repo with 0 files is registered but not yet indexed, which explains otherwise-confusing results. It also implies the return payload (paths, counts), though it doesn't say anything about ordering or size limits.

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?

Three short sentences, front-loaded with the purpose and ending on the indexing caveat. The opening rhetorical question is a small stylistic flourish rather than wasted content, but the whole thing earns its length.

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?

An output schema exists, so the description doesn't owe return-value details, yet it still summarizes the payload and handles the empty-repo ambiguity. For a no-argument, read-only listing tool this covers everything an agent needs to call it correctly.

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?

Zero parameters, so the baseline of 4 applies and there is nothing the description needs to compensate for. The schema coverage being 100% on an empty object means no additional parameter explanation is required or expected.

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 the resource (registered repositories) and states exactly what is returned: paths plus file and symbol counts. It is clearly a discovery/enumeration tool, distinct from the query-oriented siblings like search_code, get_symbol, or impact_of.

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?

It gives two explicit triggers: use it to learn valid repo values for the other tools, or after a repo was refused. That is both a positive condition and an error-recovery condition, leaving little to infer about when to reach for this instead of a sibling.

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