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

Annotations already declare the mutation/idempotency profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false). The description adds meaningful context beyond that: PATCH-style partial semantics (only passed fields change) and a plan-tier gating constraint on fast schedules. It doesn't discuss reversibility or error behavior, so it falls short of 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?

Three short sentences, each earning its place: what it does, the partial-update rule, and the plan constraint. The core action is front-loaded with zero filler.

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 6-parameter mutation tool with no output schema and full annotation coverage, the description covers the essential behavioral facts (partial update, plan gating). It omits a required-only-checkId reminder and any confirmation of return behavior, but nothing critical to correct invocation is missing.

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%, so the schema already documents all six parameters including the enum values and timezone format. The description alludes to the on/off and schedule fields but adds no syntax, defaults, or format detail beyond the schema, so the baseline 3 is correct.

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+resource ('Turn a check on or off, or change its schedule') and clearly distinguishes itself from siblings like add_checks and list_checks, which create and read rather than modify. An agent can select this without opening the schema.

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?

Provides clear context for use via the partial-update rule ('Only the fields you pass change') and a precondition ('Schedules faster than daily need a paid plan'), which tells the agent when the operation will succeed. It stops short of naming explicit alternatives or when-not-to-use cases.

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