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

Annotations already cover read-only, idempotent, closed-world and non-destructive, so the bar is lower; the description still adds real value by labeling results as estimates and disclosing the halving model (210,000-block epochs, subsidy = 50 BTC >> epoch). It does not describe output shape, but an output schema exists, so that gap is minor.

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 first two sentences are tight and front-loaded with the actual capability. The remaining half is boilerplate invocation policy ('Follow its required fields and exact choices', 'Do not pass the REST calculator field inside MCP arguments') that repeats itself and references a REST artifact the agent cannot act on meaningfully.

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?

This is a nested-object tool with three modes, conditional requirements, and enum-constrained modelVersion, and the description omits the per-mode field mapping entirely. Return values are covered by the output schema and safety by annotations, but the mode/field relationships an agent needs to construct a valid call are left to the schema alone.

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 0%, so the description must carry parameter meaning. It only states structural rules ('put tool fields inside inputs', 'supply units or modelVersion only when listed') and never explains the nested fields mode, blocks, block_time_seconds, current_height, or the conditional now_ms requirement for halving mode. What it does add is mostly formatting policy, not semantics.

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?

Names three concrete capabilities: blocks-to-duration, duration-to-blocks (using average block time), and a Bitcoin halving estimate from block height, and even states the epoch/subsidy formula. An agent can see this is a chain-timing calculator. It does not explicitly distinguish itself from the sibling buscalc_time_duration, so it stops short of 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?

Implicit routing is present ('from your average block time' vs 'from your current block height'), which tells the agent which inputs select which behavior, and 'Estimates only' sets expectations. However, there is no explicit when-to-use/when-not guidance against the time_duration sibling, and no statement of which inputs are required per mode.

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