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

Annotations only declare it a safe, non-destructive read; the description adds the pricing model ($0.02 per call via x402/MPP), the exact failure mode for an unpaid call (isError with PaymentRequired in structuredContent, no charge), and that unknown coins are refused before payment. The non-idempotent annotation is consistent with a per-call charge, and the description explains why.

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?

Front-loaded with 'Paid.' and the use condition, then progressively more detail, with no filler sentences; every clause (cost, failure mode, refusal, alternative, source) carries decision-relevant information. The pricing sentence is dense but earned.

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 paid, single-parameter read tool this covers everything an agent needs: what it returns, what it deliberately omits, cost and payment mechanics, the unpaid/unknown-coin error paths, and a cheaper sibling. Presence of an output schema makes detailed return-value explanation unnecessary, yet the description still summarizes the payload usefully.

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 the schema already documents the single 'coin' parameter with an explicit coin list. The description only restates 'ticker or name' without adding format, casing, or matching behavior beyond the schema, so it sits at the baseline.

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 verb and resource: the fair value verdict for one coin, with named deliverables (Fair Value Gap, TVR Estimated Value, scoring factors) and an explicit exclusion ('No market price or market cap'). It also distinguishes itself from the sibling get_tvr_score, so an agent can separate the two 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?

Gives an explicit triggering condition ('Use when asked whether a cryptocurrency is undervalued, overvalued or fairly priced') and names a free alternative (get_tvr_score) with what that alternative returns, giving the agent a clear decision path. The paid nature and refusal behavior further constrain when this tool is appropriate.

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