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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, openWorldHint=false), so the bar is lower. The description adds genuinely new behavioral context that annotations cannot convey: this is a paid, per-call endpoint with a stated price (3 sats / US$0.003 USDC), which materially changes how an agent should plan calls. It stops short of explaining the unpaid-response flow or failure modes, so it is not 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?

Two sentences, front-loaded with the substantive field list, followed by pricing. No filler. Slight redundancy between the title and the opening phrase, but the sentences each carry distinct information.

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?

There is no output schema, so the enumerated field list effectively documents the return payload — an important contribution. Payment mechanics are covered between the price sentence and the l402/pay_with schema descriptions. The only gap is absent guidance on sibling selection, which is a usage rather than completeness issue.

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% and both parameters (l402, pay_with) are documented in the schema, so the baseline of 3 applies. The description reinforces the payment model but adds no syntax or semantics for either parameter beyond what the schema states.

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 names a specific resource (the latest Bitcoin block) and enumerates the fields returned — height, hash, age, tx count, fees, fee-rate percentiles, size, weight, subsidy — so an agent knows exactly what it gets. It does not explicitly distinguish itself from near-siblings like bitcoin_block_header or bitcoin_block_stats, which keeps it below a 5.

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 word 'latest' implies a freshness scope, but there is no statement of when to choose this over bitcoin_block_header, bitcoin_block_stats, or bitcoin_mempool_blocks, and no exclusions or prerequisites. The agent must infer routing from the field list alone.

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