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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds the underlying REST path and docs link, which is useful for verification, but says nothing about units (sat/vB vs total BTC), aggregation method, or data granularity beyond the annotations.

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?

One front-loaded sentence captures the purpose, followed by a docs link and REST operation line. The REST path is arguably redundant with the docs link, but overall there is very little waste.

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 and annotations covering safety and idempotency, the description need not explain return values. The metric definition ('average total fees per block') plus lookback period is sufficient to call it correctly; only the unit ambiguity slightly weakens it.

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% — the single time_period parameter is fully enumerated with examples and a description in the schema. The description only restates the existence of a time period, adding no syntax or behavioral detail beyond the structured data, 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 with a quantified metric: 'average total fees per block for a time period.' This is distinguishable in wording from the fee-rate siblings (get_block_fee_rates, get_precise_fees), though the description never explicitly contrasts itself with them.

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?

No guidance on when to pick this over get_block_fee_rates, get_block_fee_rates_precise, get_precise_fees, or get_block_rewards. The agent is left to infer from names alone which fee/reward endpoint matches its need.

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