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

The description adds genuine post-condition detail beyond the annotations: no new preparation occurs and already-signed buys are unaffected. However, it does not address reversibility, what happens on a second cancel (relevant given idempotentHint=false), or required authorization, so the behavioral picture is partial.

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 with the action front-loaded and the side-effect statement immediately after; no filler. Slightly tighter phrasing could fold the two clauses into one, but the structure is efficient.

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 one-parameter, non-read-only tool with annotations covering the safety profile and no output schema, the definition supplies what an agent needs: the target identifier and the effect on existing buys. The remaining gap is the result/error behavior, which is minor at this complexity.

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% and the single `id` parameter is already described in the schema as coming from schedule_buy or list_schedules. The description's 'by its `id`' adds no meaning the schema does not already carry, so the baseline of 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?

States a specific verb and resource ('Cancel a buy plan by its `id`'), which is unambiguous against schedule_buy and list_schedules. It stops short of naming those siblings explicitly, so differentiation is inferred from the verb rather than stated.

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?

Usage is only implied: an agent can infer this applies to a plan previously created via schedule_buy, aided by the schema note. There is no explicit when-to-use, when-not-to-use, or statement of what to do instead if the plan is unknown or already executed.

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