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

Annotations already grant readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely useful provenance beyond that — the data comes from archived copies of the official pricing page and is bucketed monthly — which tells the agent the values are historical snapshots rather than live quotes. It stops short of stating coverage depth, update cadence, or pagination.

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 written sentence with the resource up front and the data source trailing. No filler, no restatement of the title.

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 one-parameter read-only lookup with no output schema, the description conveys enough about the return shape (monthly plan/price changes from archived pricing pages) that an agent knows what to expect. It could be stronger by stating how far back the history reaches or how often it refreshes.

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% for the single 'agent' parameter (it already gives a slug format and examples like cursor, claude-code), so the schema carries the parameter burden. The description adds no additional parameter meaning, making the baseline 3 correct.

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 names a specific resource (an agent's plans and prices) and a specific dimension (month-by-month change), which an agent can immediately picture. It does not, however, name or rule out the closely related siblings model_prices and current_deals, so differentiation is left to the agent.

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?

Usage is only implied: the 'month by month' framing suggests historical trend analysis rather than a current-price lookup, which weakly routes against model_prices. There is no explicit 'use this when / use X instead' statement or any prerequisite guidance.

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