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

The description discloses a non-obvious state transition the annotations cannot express: setting fire_at re-arms the reminder even if it was done or cancelled, and moves ends_at with it. That is exactly the kind of side effect an agent needs. It does not cover permissions or the response shape, but with destructiveHint/idempotentHint already declared, this is solid added context.

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?

One dense paragraph that front-loads purpose and then walks each special field in a predictable order, with no filler sentences. The opening parenthetical is the only awkward part — it reads as a clarification of alarm vs notification but adds little for an agent that has 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 an 11-parameter destructive mutation with strong schema coverage and no output schema, the description covers the risky part (re-arming a completed/cancelled reminder) and the null-reset semantics for every optional field. It stops short of describing the returned object, which is a minor gap given there is no output schema to lean on.

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 already 82%, so the baseline would be 3; the description earns an extra point by spelling out null semantics the schema leaves implicit — null color/icon/location reverts to the default, null sound returns to the user's default sound, null ends_at removes the end. It also restates the reminders-only constraint for fire_at and ends_at, keeping the enum-heavy fields interpretable without opening the schema.

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?

States a specific verb ('Change') and resource ('a reminder'), and enumerates the mutable facets (texts, location, colour, icon, sound, plus the title/body fields). An agent can tell it apart from create_alarm, cancel_alarm and list_alarms, though the parenthetical about 'a notification' is slightly muddling and no sibling is named explicitly.

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?

'Pass only the fields to change' is a genuinely useful partial-update rule, and the fire_at note implies when this tool's re-arm behavior matters. But there is no explicit when-to-use vs create_alarm/cancel_alarm/rename_agent guidance, so routing must be inferred from the tool name.

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