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

Annotations already declare readOnlyHint=false and destructiveHint=false, so safety is partly covered; the description reinforces and extends this with concrete behavior — appends to the end unless sortOrder overrides, and cannot drop existing choices. It adds real context beyond the annotations, though it doesn't mention auth/permission requirements.

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 tight sentences, front-loaded with verb+resource+scope, then the safety contrast, then the parameter nuance. Every sentence earns its place with no padding.

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?

Covers the operation's key nuances (safe append, price format, ordering) for a write tool with no output schema. It doesn't describe the success response, a minor gap, but nothing needed to invoke correctly 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 coverage is 100%, so baseline is 3, but the description adds genuine meaning: price is a human-readable amount ('0.70'), omitting it still prints a free choice on the receipt, and sortOrder controls append vs position. These go beyond the schema's own text.

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 ('Add one choice to an existing modifier') and scopes it precisely ('leaving the rest alone'). It explicitly distinguishes itself from update_modifier, so an agent can route without opening either 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?

'This is the safe way to extend a modifier — unlike update_modifier, it cannot drop anything' names the alternative and the condition that selects this tool. The add-vs-update distinction is spelled out rather than left to inference.

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