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

Annotations already declare readOnlyHint=false and destructiveHint=true, so the mutating nature is known. The description adds real value by disclosing the cross-tool effect of the default, but does not say whether the setting persists across sessions, what happens to previously set defaults, or what the response confirms — notable gaps for a destructiveHint=true operation.

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 short sentences, front-loaded with the effect and followed by the input guidance. No filler and nothing that could be cut without losing meaning.

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 single-parameter setter with an output schema, annotations, and full schema coverage, the description covers purpose, effect, and value sourcing. Nothing an agent needs in order 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?

Schema coverage is 100%, so the baseline is 3, but the description adds the accepted value forms (label or id) and, more usefully, points to whatsapp_list_accounts as the source of valid values — information the schema does not contain.

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 (choose/set) and resource (default WhatsApp account), and crucially explains the effect: it changes which account the whatsapp_* tools use when no `account` is supplied. This distinguishes it clearly from whatsapp_list_accounts and from the individual whatsapp_* action tools.

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 the triggering condition explicitly ('when no `account` is given') and routes the agent to whatsapp_list_accounts to obtain valid labels/ids. It lacks an explicit when-not statement (e.g., that per-call `account` arguments override this default), but the usage context is clear.

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