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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds value beyond that by naming the returned fields (slug, display label, timezone, hub website) and by giving the 'website is the source to cite' convention, which is behavior an agent cannot infer from 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?

Three sentences, front-loaded with scope, then the returned fields, then the downstream slug contract and citation note. No filler and no repetition of annotation data.

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?

For a zero-parameter enumeration tool with rich annotations and an output schema, the description covers what the tool does, what it returns, how to reuse the slug, and the citation convention. Nothing an agent needs to call it correctly is missing.

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?

The tool takes zero parameters, so the baseline is 4. The description correctly spends no space on parameter meaning and instead points at the output field (slug) that other tools consume.

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 plus resource ('List the cities (hubs)') and it enumerates the exact coverage set (mygn.de Hamburg/München/Oldenburg + Umland, rundown.city San Francisco), which distinguishes it from siblings like list_categories or search_events. An agent knows immediately what domain this enumerates.

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 explicitly states the downstream contract: 'Pass the slug as hub to the other tools', making it clear this is the prerequisite lookup for hub-scoped calls. It stops short of naming a specific sibling as the alternative or stating when not to call it, so it is clear context rather than a full routing rule.

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