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

Annotations already cover safety (readOnly, idempotent, non-open-world), and the description adds material context they cannot express: the call is metered and costs 2 sats / US$0.002 USDC. That cost signal is genuinely useful for an agent deciding whether to call it. The description does not explain the payment dance itself (invoice, L402 token), though the l402 and pay_with parameters carry part of that.

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: the first front-loads what the tool does and exactly what comes back, the second states the cost. No filler, nothing repeated from the 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?

With no output schema, the description correctly enumerates the return fields (validity plus reason, type, witness version, scriptPubKey), which is what an agent needs to use the result. The metered-payment flow is only partly covered, but the supporting parameters and annotations fill most of that gap.

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 coverage is 100%, so addr, l402 and pay_with are all documented in the schema, and the description adds no further meaning about them. The pricing sentence loosely motivates pay_with but does not clarify how the two payment modes behave. 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 pair and resource ('Validate and classify one Bitcoin address') and enumerates the returned classifications (P2PKH, P2SH, P2WPKH, P2WSH, P2TR), so the scope is unmistakable. It stops short of separating itself from look-alike siblings such as bitcoin_address_risk or watch_bitcoin_address, leaving the agent to infer that this tool is validation rather than risk scoring or monitoring.

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?

'One Bitcoin address' implies the single-address case, which implicitly contrasts with the batch and monitoring siblings, but there is no explicit when-to-use or when-not-to-use statement. An agent must infer that this is the right call for a cheap validity/type check rather than a risk assessment.

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