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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: it discloses that only block 0 is a real projection while blocks 1+ are a fee-tier approximation, warning the agent about data fidelity.

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 tight sentences front-load the purpose and the important block-0 caveat. The trailing docs link and 'REST operation: GET /api/v1/fees/mempool-blocks' are brief but boilerplate that adds little for an agent already given the tool schema.

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?

An output schema exists, so return-value structure needn't be spelled out, and the description still conveys the meaning of block 0 versus later blocks. Combined with a zero-parameter, annotated, read-only operation, this is nearly complete; only explicit sibling routing 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?

The tool takes zero parameters, so the baseline is 4. Nothing in the schema needs explanation, and the description correctly does not invent parameter guidance.

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 resource ('Projected blocks') and its purpose ('for fee estimation'), plus the key structural distinction that block 0 is Core's actual next-block selection while blocks 1+ are approximations. It doesn't name which sibling to use instead (e.g., get_precise_fees or get_block_fee_rates), so sibling differentiation is implicit rather than explicit.

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?

'For fee estimation' implies the use case, and the block-0-vs-1+ note hints at when the data is authoritative versus approximate. However, there is no explicit statement of when to prefer this over the many sibling fee/block tools (get_precise_fees, get_block_fee_rates, get_mempool), leaving the agent to infer.

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