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

Annotations already declare a safe, idempotent, non-destructive read, so the safety profile is covered. The description adds that the index reports median and minimum values per month/data tier, but says nothing about the time span covered, refresh cadence, or output shape, which matters more given there is no output schema.

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 short sentences, with the core content (what the index compares) stated first and the use case second. Every clause carries information and there is no 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?

For a zero-parameter index tool, the description conveys what is measured and when to reach for it, and the annotations cover the rest of the safety profile. The remaining gap is return-value behavior (time range, granularity, format), which is not covered by an output schema and is only partially implied.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate — the baseline for a no-parameter tool applies. The description correctly implies the query is unfiltered by any argument, consistent with the empty schema.

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 (MVNO price index) and states precisely what it aggregates: monthly median and minimum lifetime-plan prices compared per data tier. This is far more than a restatement of the name, but it never explicitly distinguishes itself from the sibling plan_price_history or recent_price_changes.

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?

It gives a concrete usage condition — trend questions such as 'are MVNO prices rising?' — which tells the agent when this tool applies. However, it offers no exclusions and does not name the alternative tools (plan_price_history, recent_price_changes) that could be confused with it.

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