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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered; the description goes beyond by disclosing the auth-dependent behavior (connected app reads the stored selection, API key always returns selected: null). It also hints at an accompanying sites list when no selection exists. The only soft spot is that the exact return shape is described informally rather than precisely.

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?

Front-loads the core question, then branches on the two deployment modes, then closes with the alternative tool — a clean three-move structure. No sentence is redundant and nothing is buried.

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 present, the description carries the burden of describing return values and does so: selected is null when nothing is chosen, the available sites are included, and API-key connections always yield null. Combined with the sibling routing, an agent has everything needed to call this correctly and interpret the result.

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 there is nothing for the description to disambiguate and the baseline is 4. The description correctly avoids inventing parameters and instead spends its words on return semantics.

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 and resource — reporting the currently selected site for this connection — and frames it around the exact user question it answers ("which site am I on?"). It is clearly distinguishable from list_sites (enumerate choices) and select_site (mutate the selection), both named in the text.

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?

Names the intent that selects it, then explicitly redirects the alternative case: "To pick or change the site, call select_site with one from list_sites." Both the when and the when-not are present, with the correct sibling for each.

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