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 adds substantive context beyond that: results are limited to companies visible to this AccountsOS account, the default company is marked, and the output is intended to feed a `company` parameter into other tools.

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 compact sentences, front-loaded with the core action and scoping, followed immediately by the operational instruction. No filler, and every sentence conveys distinct information.

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 listing tool with annotations covering safety and no output schema, the description gives everything needed: what is listed, whose visibility constrains it, that a default is marked, and how to use the results in later calls.

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 covers everything and the baseline is 4. The description adds useful downstream semantics by explaining that the listed company identifiers are intended to be passed as `company` to other tools.

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 ("List the companies"), scopes it to what the authenticated AccountsOS account can see, and clarifies that for an accountancy practice these are its clients. The parenthetical and "default one marked" make it distinguishable from lookup_company, link_company, and update_company, which all act on a single known company.

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 an explicit trigger ("Call this first when the user has more than one company") and a follow-up behavior ("then pass `company` to the other tools"). It does not explicitly contrast against lookup_company when a single company is already known, but the multi-company condition is a clear contextual rule.

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