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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds meaningful behavioral context beyond that: results are normalized to price-per-100-credits and converted into a single currency, which tells the agent how values are shaped. It omits pagination/return-format detail, but the output schema covers that.

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 tightly written sentences with zero waste; the scope and normalization are front-loaded and the example follows naturally.

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?

With an output schema present, return values need not be explained, and the description covers purpose, scope, and normalization adequately. The main omission is explicit sibling routing, which keeps it from a 5.

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 78%, so the schema largely documents parameters itself. The description reinforces the normalization/currency concept but adds no per-parameter syntax or defaults beyond what the schema already states, so baseline 3 is appropriate.

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 specific verb and resource ('Compare credit pack prices') and clarifies scope ('extra usage credits sold on top of a subscription') plus the normalization ('price per 100 credits in one currency'). This distinguishes it well from a generic price tool, though it never explicitly contrasts with the sibling compare_prices.

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?

An example question ('where are ChatGPT credits cheapest?') implies the intended use case, but there is no explicit guidance on when to use this versus compare_prices, get_region_prices, or other siblings, and no stated exclusions.

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