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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds a genuine behavioral detail – the exact computation (activity MB × days × Wi-Fi factor × 1.15 buffer, rounded up) – which explains how results are derived, though it omits units, rounding output format, and what 'daily MB per activity' values are assumed.

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?

A single tightly-packed sentence with no filler, and the formula is front-loaded. The external-site reference is of marginal value to an agent but does not pad the text.

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 3-parameter tool with no schema descriptions and no output schema, the description should specify input units, the meaning of the wifi enum, and the shape/units of the returned estimate. It leaves all of that implicit, so an agent cannot confidently populate or interpret the call.

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 0% across three parameters, so the description is the only source of meaning. It names 'days' and 'Wi-Fi factor' but never explains the wifi enum values (rarely/sometimes/often), the 1–180 day range, or the activity vocabulary, leaving real gaps.

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 gives a formula rather than stating what the tool produces; a reader must infer from the expression that it estimates mobile data consumption for a trip. The name and title ('estimate_data' / 'Estimate data needed') carry most of the purpose, and no verb+resource statement distinguishes it from get_plan or recommend_plan.

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?

No guidance on when to use this versus siblings like recommend_plan or get_plan, and no prerequisites or exclusions. The reference to an external calculator implies a comparison use case but never says when an agent should prefer this tool.

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