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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false. The description adds meaningful behavioral context: language applies to all future outputs and renders, takes effect on the next call, and is account-wide. This goes beyond the annotations, providing clarity on scope and timing.

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 compact but thorough, using inline definitions for the parameters. Each sentence serves a purpose: the main action, parameter explanations, usage guidance, and scope/timing. No wasted words, though it is slightly longer than strictly necessary.

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 settings-update tool with no output schema, the description covers all essential aspects: what changes, how (partial updates), scope (account-wide), and timing (next call). It lacks permission or error details, but these are not critical for this tool. It is complete enough for an agent to call correctly.

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% with descriptions for each parameter. The description enhances this by explaining language in detail ('the language EVERY ad, script, plan and answer is written in from now on', with plain-English examples) and clarifying that theme is 'dark' or 'light' and watchEmail is the weekly competitor-watch email. This adds nuance not captured in the schema.

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 clearly states what the tool does: 'Change this account's app settings.' It enumerates the three exact settings (language, theme, watchEmail) and clarifies scope with 'Account-wide (every brand)'. This distinguishes it from the sibling get_settings (read-only) and other set_* tools that target specific features.

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 gives practical usage guidance: 'Only pass what you are changing' and 'Account-wide (every brand), and it takes effect on the next call.' It implies when to use (when altering account settings) but does not explicitly state the alternative for reading settings (get_settings). Still, the context is sufficient for an agent to choose correctly.

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