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

Annotations already declare a non-read-only, non-idempotent, non-destructive mutation, so the key open question is what a repeated call does (duplicate guests or replace?) and whether adding guests alters dinner planning/recipe sizing. The description says nothing about either, adding almost no behavior beyond the annotation block.

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?

Two short sentences, front-loaded with the core action and followed by the one non-obvious usage rule. No filler, though the guestNames sentence could be read as belonging to parameter docs rather than purpose.

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?

With seven parameters and no output schema, the description covers the multi-day case and named guests but omits the consequences of the write: duplicate handling, whether existing guests are appended or replaced, and whether the plan or shopping is affected. Adequate but leaves real gaps for a mutation tool.

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%, so baseline is 3, and the description earns an extra point by explaining the guestNames-versus-counts distinction ('name the household's usual guests instead of counting them') and that endDate turns a single dinner into a multi-day visit.

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 names a specific verb and resource ('Add guests for dinner') and clarifies the multi-day variant via endDate. It is clear enough to distinguish from siblings like mark_eating_out or mark_away, though it never explicitly contrasts itself with them.

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?

There is usage guidance for one decision — put recurring household guests in guestNames rather than inflating adultCount/childCount — but no statement of when to prefer this tool over adjacent ones (e.g. mark_eating_out, delete_meal_event) or when not to use it.

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