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

With no annotations, the description carries the full burden, and it does disclose the most consequential behavior: this is a paid tool at 0.001 USDC per call via x402, and conversions are exact on big numbers rather than float-rounded. That cost signal is exactly the kind of thing an agent must know before calling. It does not cover error behavior or what an invalid unit pair returns, which keeps it from a 5.

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 sentences, the capability first and the price second. No filler, no restatement of the tool name, and the cost – the one fact most likely to change agent behavior – is surfaced early rather than buried.

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?

Five parameters with full schema descriptions and a detailed paymentProof field covering the 402 handshake, so the description does not need to repeat that flow. It covers what to convert, the supported unit systems, and the cost. It omits only edge behavior such as unsupported units or default-decimal assumptions, which is a minor gap for a simple conversion utility.

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 the baseline is 3, and the description earns an increment by explaining why 'value' is a string – 'exact big-number conversion' tells the agent precision matters and floats are unacceptable – and by clarifying that 'any token with a given number of decimals' is what the decimals parameter governs. That is meaning beyond the field-level texts.

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 precise verb and resource (exact big-number conversion) and enumerates the concrete unit systems handled: wei/gwei/ether, lamports/SOL, and arbitrary decimal tokens. This is far more than a restatement of the name. It stops short of 5 because it does not explicitly differentiate itself from adjacent siblings like fx_rates or crypto_price, though the on-chain base-unit framing is implicitly distinct.

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?

Usage is implied by the domain framing – you call this when you have a raw on-chain amount and need a human-readable value or vice versa. There is no explicit when-to-use statement, no exclusion of alternatives (e.g. when to prefer crypto_price for fiat values), and no note on the 402 retry workflow in the description itself. Adequate but leaves routing to inference.

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