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

Annotations already declare destructiveHint=true and non-idempotent behavior, but the description adds real context beyond them: revision-based (optimistic-concurrency) writes, a permission gate on locale/voice fields, and a scope boundary ('internal system prompts are not exposed through MCP'). It still doesn't say what happens when the revision is stale or whether omitted fields are cleared, which matters given the destructive hint.

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 short sentences, front-loaded with the action and fields before moving to prerequisites and limits. The final sentence on system prompts is slightly tangential but earns its place as a scope boundary, so nothing is truly wasted.

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 destructive, non-idempotent mutation with a nested `changes` object and an output schema already declared, the description covers the essentials: what it writes, the revision prerequisite, and permission requirements. The main residual gap is error/staleness behavior on a bad revision and merge-vs-replace semantics.

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?

With 0% schema description coverage, the description compensates well by mapping its wording onto the params: profile→changes.name, language→changes.call_locale, voice defaults→changes.voices_by_locale, and revision→the get_account-supplied token. It doesn't clarify whether `changes` is a partial merge or full replacement, nor what a null name or a locales/voices key mismatch means.

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 and resource ('Update supplied profile, language and voice defaults') and enumerates the field groups the tool mutates, so an agent knows exactly what the call changes. It does not explicitly differentiate itself from update_agent, which is the nearest sibling, so it falls short of a 5.

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?

It gives a concrete prerequisite ('using the revision from get_account') and a permission condition ('Language and voice defaults require configuration permission'), which tells the agent how to prepare and when the call may fail. It stops short of explicit when-not-to-use guidance or naming alternatives beyond get_account.

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