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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable context beyond annotations: the cost (2 credits) and the paid-plan capabilities including 172 currencies and additional metrics. It stops short of describing data freshness or source latency, preventing a 5.

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?

The core purpose is front-loaded in the first sentence, and the paid-plan details follow in a second sentence. The only waste is the repeated tool name at the beginning ('Bitcoin Price: Bitcoin Price...') and the long enumeration of paid metrics, but overall the structure is clear and appropriately sized for the tool's complexity.

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?

Given a simple read-only price tool with full schema coverage, annotations, and an output schema, the description is nearly complete: it covers core purpose, default currency, paid-plan limits, and cost. It omits optional details like data source or latency, but nothing essential for correct invocation is missing.

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%, so the input schema already fully documents the daily, hourly, and currency parameters. The description reinforces currency behavior ('USD' default, '172 currencies' on paid plans) and history options, but adds no format details or constraints beyond what the schema already provides. Baseline 3 is appropriate when the schema does the heavy lifting.

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 states a specific verb and resource: 'fetches the current Bitcoin price, recent movement direction, and update timestamps in USD.' It clearly distinguishes this from sibling price tools like EthereumPrice and GoldPrice by naming Bitcoin explicitly. The only minor weakness is the redundant 'Bitcoin Price: Bitcoin Price...' opening.

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 implied by the self-evident name and the stated purpose of fetching Bitcoin price, but the description does not explicitly say when to use this tool versus alternatives such as EthereumPrice or CurrencyRate. The paid-plan note hints at capability tiers but does not provide direct when-to-use or when-not-to-use guidance.

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