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

readOnlyHint=true already tells the agent this is a safe read, so the description adds value beyond annotations by disclosing the empty-state behavior — when no guide is set it returns a note rather than an error, and the agent should switch to default rules. It does not describe the shape or length of the returned guide, which is the main remaining gap, but the missing-guide handling is the operationally important part and is covered.

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, front-loaded with the purpose and then the gating condition and fallback; nothing is padding. A hard line break mid-sentence ('researched / before you write to them') slightly interrupts the read, and the 'outreach craft skill' reference assumes the agent knows that skill, which is the only reason it is not a 5.

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-required-parameter read tool with no output schema, the definition covers purpose, gating condition, and empty-state fallback — enough for an agent to call it correctly. It could go one step further and describe what a returned guide looks like, but that is a minor omission given the annotations already establish the safety profile.

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 description coverage is 100% and the single on_behalf_of parameter is documented in detail in the schema itself, including its source (list_agency_clients) and the omit-for-own-account default. The description mentions nothing about this parameter, which is acceptable given the schema carries it, so the baseline 3 applies with no added meaning.

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 gives a specific verb and resource ('Return the user's personalization guide') and then defines what the resource actually contains ('how they want a person researched before you write to them'), which distinguishes it in substance from guide-adjacent siblings like get_writing_style_guide or get_skill_guide. It stops short of explicitly naming a sibling to route against, so a 4 rather than 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 states an explicit precondition ('Call this only when you are going to personalize a message'), an instruction on what to do with the result ('follow the returned guide'), and a documented fallback path ('fall back to the default research rules in the outreach craft skill') for the empty case. Both the when and the when-not are covered, so no inference is required.

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