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

Adds substantial behavior beyond annotations: partial update ('Only the fields sent are changed'), that logo and uploaded font files are preserved because they cannot be set over MCP, and the downstream effect on future ebooks. Annotations already flag destructiveHint=true, so this extra scoping context is exactly what's needed.

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 tight sentences, front-loaded with what changes, then the preservation constraint, then the impact scope and the alternative tool. No wasted words.

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?

Mutation tool with no output schema, but annotations plus description fully cover safety, partial-update semantics, and side effects. An agent has everything needed to call it 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 88% and params are well-described, so the schema carries most of the burden. The description adds the partial-update semantics and the preservation of logo/font files, but adds nothing about specific fields like the colour hex format or the links map.

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?

Specific verb+resource: 'Change the name, colours, fonts or links of one of the caller's saved Brand Themes', and even names the source for ids (list_brand_themes). An agent can distinguish it from create_brand_theme and update_ebook immediately.

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?

Explicitly routes the agent: use this to change the theme itself, but 'To restyle ONE ebook, use update_ebook's theme instead.' Also clarifies the blast radius (affects every ebook later applied, and new ebooks if it's the account default).

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