How much fits in a phone storage tier

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

Annotations already declare readOnlyHint=true, confirming it's a safe read. The description adds value by noting corrections for OS/filesystem overhead and that it is 'Backed by Cleanor Labs measured per-item sizes,' which provides transparency beyond annotations. No contradictions.

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 sentences, front-loaded with the core purpose. Every sentence adds value: purpose, data source, and use cases. No redundancy.

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?

Given the tool's simplicity (2 parameters, no output schema) and three siblings, the description covers everything: what it does, how it works, and when to use it. No gaps.

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% with both parameters described. The description adds meaning by linking 'storage_gb' to 'advertised storage size' and 'content' to 'photos or minutes of video,' reinforcing the enum values. No additional schema is needed.

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?

The description clearly states the tool's function: counting photos or video minutes that fit in a given storage size, with real OS/filesystem overhead. It uses specific verbs and resources (e.g., 'How many photos or minutes of video actually fit') and distinguishes from siblings like 'image_format_savings' and 'optimize_image'.

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?

The description provides explicit use cases: 'Use for realistic sample copy, dashboards, or "how many photos fit in 128 GB" answers.' It does not explicitly state when not to use or mention alternatives, but the context is clear enough for an agent.

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