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

Annotations already declare destructiveHint=true, idempotentHint=true, and openWorldHint=false, so safety and repeatability are covered. The description adds genuinely new behavior: that the operation is a merge rather than a replace, and that null/empty string clears text fields. It does not explain what the destructive aspect means in practice (e.g. clearing values) or what a failure looks like, which keeps it from a 5.

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 sentences, front-loaded with the verb and resource, and the second sentence carries the most decision-relevant rule (partial update plus clearing). The long field enumeration is slightly list-like but each item maps to a real parameter, so little is wasted.

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 14-parameter mutation tool with no output schema, the definition covers the essential semantics: which fields can change, that unpassed fields are untouched, and how to clear text. Missing details such as the required id, error behavior, or how date/start_time interact are only partially covered (start_time needs a date is in the schema), so it is strong but not exhaustive.

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 86%, so the schema already documents nearly every parameter, including enums, formats, and timezone rollover for end_time. The description mostly paraphrases field groups ("whether guests see it", "whether it has fixed seats (a seating plan)") rather than adding syntax or constraints beyond the schema, so the baseline 3 applies.

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?

"Changes a moment" gives a specific verb and resource, and the following field list makes the scope concrete (name, kind, date/times, place, capacity, visibility, seating, notes, uninvited text). It is clearly distinct from add-moment and delete-moment by implication, though it never names 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?

The description implies the use case for partial updates ("Only the fields you pass change") and explains clearing semantics, which is real guidance on how to invoke it. It does not say when to choose this over add-moment/delete-moment or state any preconditions such as the moment already existing.

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