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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=false, so safety is covered. The description adds real context the annotations do not: this is a partial/merge update where only supplied fields change, and it is user-initiated. It does not mention failure modes or whether changes are reversible, so it stops short of 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?

A single front-loaded sentence listing the fields, followed by a short imperative clause. Every phrase carries information and nothing is repeated from the schema.

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 five-parameter partial-update tool with no output schema, the definition covers scope, trigger and update semantics adequately. Missing only edge-case behavior (unknown sphere name, effect of clearing sections) which an agent would want before calling.

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 80%, so the schema already explains color format, sphere identification and hidden_from_day semantics. The description's only addition is the optionality/partial-update framing, which does not compensate for the undocumented name constraints (min/max length) — baseline 3 is appropriate.

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 and enumerates the four mutable fields (name, color, sections, hidden_from_day), so the agent knows exactly what this mutates. It does not explicitly distinguish itself from archive_sphere or add_sphere, which is the only thing keeping it from 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?

"When the user asks" is vague trigger guidance and no alternative is named — e.g. archive_sphere for removal or a hide-only path. The partial-update instruction ("Send only what changes") implies the update pattern but does not state what happens to fields that are omitted or what to do when the sphere is not found.

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