List the On the Cheap sites

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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds value by stating 'This server reads them all' and 'Read-only,' reinforcing the read-only nature, and by explaining the relationship to other tools (no default site). It doesn't describe return format or pagination, but for a list-all tool with no parameters, the behavioral context is largely complete. The description does not contradict 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 three sentences, each earning its place: what it lists, why it matters (site key), and when to use it. It is front-loaded with the core action and resource, and there is no fluff or repetition of the title.

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, read-only list tool with no output schema, the description is complete. It tells the agent what it returns (city names and site keys), why that matters (site selection for other tools), and when to call it. The annotations cover safety and idempotency. Nothing an agent needs to invoke 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 has zero parameters, so the schema is trivially complete (100% coverage). The description adds meaning by explaining what the output is used for (the `site` key to select a city in other tools), which is valuable context beyond the empty schema. Baseline for 0 params is 4, and the description earns it by clarifying the purpose of the returned keys.

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 states a specific verb ('List'), a specific resource ('every city in the on the Cheap network'), and the key output ('the `site` key used to select it'). It also distinguishes itself from sibling tools by explaining that this is the starting point for selecting a site, which is unique among the listed siblings.

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 says when to use this tool: 'start here when you do not already know which key covers the city the user means.' It also explains the context that every other tool takes a `site` argument and there is no default, which effectively tells the agent to use this tool before others when site is unknown. This is clear usage guidance with an implicit alternative (other tools) and a condition.

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