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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so the safety profile is covered. The description adds real context about output shape (the percentile set and rounding) that goes beyond the annotations, though it says nothing about rate limits or auth.

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?

Front-loads the operation and return set in one tight sentence, then a docs link and REST path. No filler; every element is informative.

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 a full output schema and rich annotations, the description needs only to state what is fetched and how it differs from the precise variant, which it does. Minor omission of any auth/rate-limit context 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 coverage is 100% and the enum with all valid time periods is fully documented in the schema, so the schema does the heavy lifting. The description adds no meaning to `time_period` beyond what is already structured, so baseline 3 applies.

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 and resource ('Get block fee rate percentiles') and enumerates exactly what is returned (min through max). It also distinguishes itself from the sibling get_block_fee_rates_precise by noting the whole sat/vB versus `/precise` 3-decimal variant.

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?

The parenthetical '(`/precise` for 3 decimals)' implicitly routes the agent to get_block_fee_rates_precise when finer precision is needed. There is no explicit when-not or prerequisite guidance, but the alternative is clearly signposted.

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