utilpeek: live FX rates from Base stablecoin pools (EUR, GBP, MXN, BRL, CAD, SGD, ZAR, IDR) with ECB deviation, plus exchange bid/ask for the majors

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

Goes far beyond the readOnly/idempotent/openWorld annotations: thin pools are segregated into `thin` never as a rate, cache TTLs (pools 15s, exchange 60s), failed fetches land in `errors`, unknown pairs return a 422 that is not charged, latency 2-4s, and pricing/free-tier terms. This is unusually rich disclosure for a read tool.

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-loads the decision-relevant clause (when to use, sibling alternative) before mechanics. It is a dense single block, but nearly every clause (thin, errors, cache TTLs, 422, price, latency) carries information an agent needs, so little is wasted.

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 an output schema present, the description still names the key return fields (exchange_quotes, age_s, thin, errors) and the failure/pricing/caching envelope. For a two-param, zero-required tool, an agent has everything needed to call and interpret it correctly.

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 schema already documents pairs (market convention, omit-for-all, USDJPY/AUDUSD behavior) and amount_usd (100-100000, default, thin threshold). The description mostly restates these, adding little syntax or format meaning beyond the schema, so the baseline 3 applies.

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+resource and scope: 'price an amount of EUR... in USD now, not at the ECB fix'. It explicitly names the sibling it is not (get_fx_rates) and the source (on-chain stablecoin pools on Base), so an agent can distinguish it from alternatives without opening any 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 explicit when-to-use ('must price... now, not at the ECB fix') and when-not ('For the ECB fix or a past date use get_fx_rates'). Nothing is left to inference, and the alternative condition is spelled out.

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