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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered. The description adds one genuinely new behavioral fact — the result mirrors the free website forecast, implying a deterministic model rather than live account data — but says nothing about assumptions, precision, or the model behind the 'usage_profile' buckets. Adequate, not rich.

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 sentences, zero filler. The positive definition comes first and the negative scoping second, with the website-parity anchor front-loaded so the agent immediately knows what class of tool this is.

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?

The output schema exists, so return values need no prose, and annotations cover the mutation/safety story. What remains missing is the semantics of the categorical input and the units for the numeric inputs — meaningful given 0% schema coverage — but the definition plus schema is otherwise sufficient to invoke correctly.

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%, so the description carries the burden, and it only partially meets it: it names plan size, usage profile and days elapsed conceptually but gives no units (GB, percent, days), no ranges, and no meaning for the light/moderate/heavy enum. An agent could call it, but would be guessing at what 'moderate' actually models.

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 (estimates when a threshold is reached) and enumerates the three driving inputs, so the agent knows exactly what computation happens. It does not name the closest sibling (estimate_data_usage), so cross-tool routing still requires inference, but the task itself is unambiguous.

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?

Explicitly carves out when-not: 'Does not set alerts, monitor an account, or read carrier usage,' which rules out monitoring/alerting intents. No positive alternative is named (e.g., estimate_data_usage for raw usage figures), so the exclusion is clear but the redirect is not.

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