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 context beyond that: it is a paid endpoint ($0.003 USDC via x402 on Base/Solana/Arc, failed calls free) and the response includes documented calculation methodology. It does not cover return shape or how the date/days inputs interact, but the output schema handles returns.

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?

Purpose and metric definition are front-loaded in the first sentence, then methodology note, sibling routing, and pricing. Every element is relevant, though the sibling blurbs are wordier than needed and pricing sits at the end where it is easy to miss.

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?

For a two-optional-parameter read-only metric tool with an output schema, the description covers purpose, measurement definition, cost, and sibling routing. The only remaining gap is precedence between 'date' and 'days', which is minor given full schema coverage and a documented output shape.

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 both parameters are already documented with format, default, and bounds. The description only adds the either/or framing ('recent days or a specific date'), which marginally clarifies intent but adds no format or precedence detail beyond the schema.

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, named metric ('Bitcoin Coin Days Destroyed') with what it measures ('economic weight of transferred coins weighted by their dormancy period') and the retrieval scope ('recent days or a specific date'). It explicitly names two sibling tools and their different purposes, so an agent can distinguish it without opening schemas.

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?

Gives clear routing guidance for the two Bitcoin siblings: use crypto_btc_chain_tips for stale/orphaned blocks and sidechain forks, and crypto_btc_block for detailed block summaries by height or hash. What's missing is guidance on when to pick 'days' versus a specific 'date', or when a different CDD-style metric would be preferable.

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