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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the safety profile is covered, yet the description adds real value: it discloses the update is silent (no push notification), that the value replaces rather than increments (idempotent, safe to repeat), and that 0 clears the badge. It stops short of mentioning auth requirements or rate limits, but the added behavioral context is strong.

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?

Front-loads the core action and resource, then layers in the alternative-tool routing, the clearing rule, the replace-not-add semantics, and targeting. Every sentence carries distinct information and the closing instruction on how to phrase results is useful rather than 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?

With an output schema present, return values need not be explained. Given only two parameters and full schema coverage, the description covers purpose, alternative-tool routing, edge cases (0 clears, replacement semantics), and scoping, so nothing needed to call it 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 description coverage is 100%, so both parameters are already documented in the schema. The description's notes on Send 0 to clear and optional channel slugs largely restate what the schema already says, adding no syntax or format detail beyond it, which fits the baseline 3.

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 (set) and resource (App Icon Badge number) with concrete examples of what the count represents. It explicitly distinguishes itself from send_push_notification, so an agent can pick the right tool 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?

Gives explicit when-to-use routing: this tool for silent badge updates, send_push_notification when the user should be alerted, and the badge field of that tool to do both at once. Also documents the Send 0 to clear case, leaving little to inference.

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