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

The readOnlyHint annotation already covers the safety profile. The description adds valuable behavioral context: an unset guide returns a note, the agent should fall back to default research rules, and the returned guide should be followed. It does not detail the output structure, but with no output schema present it still conveys the key return states.

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 sentences, each earning its place: what the guide is, when to call the tool, and what to do when no guide exists. The trigger condition is front-loaded near the start. There is no redundant restatement of the title or annotations.

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 retrieval tool, the description fully covers invocation trigger, the returned guide, the absent-guide case, and the fallback behavior. There is no missing information that would prevent an agent from calling it correctly. The lack of an output schema is acceptable because the description captures the two possible return states.

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 takes zero parameters and the schema already makes this explicit with an empty properties object and 100% coverage. No parameter documentation is therefore necessary. The description appropriately focuses on invocation context rather than parameters.

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 it returns the user's personalization guide and defines its content: how they want a person researched before writing. This verb-resource pair is distinct from sibling get_* tools like get_skill_guide and get_writing_style_guide. The phrase 'before you write to them' reinforces the tool's unique role in message personalization.

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 explicitly says to call this only when personalizing a message, establishing a clear trigger condition. It also documents the fallback behavior when no guide is set, referencing the outreach craft skill as the alternative path. This leaves no ambiguity about when and how to use the tool.

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