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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful behavior beyond that: a per-call price of $0.002 USDC via x402, the accepted payment chains, and that failed calls are not charged — a cost-risk fact an agent must know before invoking. It does not cover rate limits, caching, or error behavior for an invalid hash/height.

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 purpose and source are front-loaded, followed by the field list, the sibling routing, then pricing — a sensible order with no filler sentences. It is slightly dense and the field enumeration partially duplicates the output schema, but every sentence carries usable signal.

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 listing return fields is redundant rather than required, and the annotations carry the read-only/open-world profile. With those covered, the description supplies the remaining decision-critical pieces: data source, sibling alternatives, and cost and billing model. The only unresolved point, which param to pass, is a minor edge case for a single-block lookup.

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 schema already explains that 'hash' is a 64-character hex string and 'height' is a height number. The description only restates 'by height or hash' and adds no semantics on mutual exclusivity, precedence if both are provided, or the fallback when neither is given. 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 gives a specific verb+resource ('Detailed Bitcoin block summary'), names the data source (mempool.space), and enumerates the returned fields (size, weight, tx count, fees, subsidy, reward, pool, coinbase message). It also explicitly distinguishes itself from crypto_btc_mining_pools and crypto_btc_blocks_range, so an agent can route without opening either schema.

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?

It names two concrete alternatives with the condition that selects each ('when you need ... pool hashrate and block shares over 24h, 3d' and 'when you need up to 144 consecutive blocks descending'), which is strong routing guidance. The gap is that it never says how to choose between the two identifying parameters or what happens if neither is supplied, which is usage guidance an agent needs for a 0-required-param tool.

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