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

With no annotations, the description carries the behavioral burden well by disclosing the official ECB rate source, the 90-day date window, the business-day fallback rule, and a per-call price via x402. It omits details such as payment/auth mechanics, rounding behavior, and error cases, 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?

The description is compact and front-loaded: conversion purpose, rate source, supported date range, fallback behavior, and pricing. Each clause adds useful information, with no redundant or filler sentences.

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 tool with no annotations and no output schema, the description gives enough context to select and broadly invoke it: rate source, currency universe, date constraints, fallback, and pricing. It is not fully complete because it does not enumerate or define accepted currency codes, date input format, or the conversion result format.

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 reported at 100%, but the schema descriptions are placeholders like 'from', 'to', and 'amount'. The tool description adds meaning for the currency pair and especially the date parameter, including the 90-day window and fallback behavior, but it does not specify currency code format, date format, amount precision, or same-currency behavior.

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 states a specific verb and resource: convert an amount between two currencies. It also identifies the rate source (official ECB euro reference rates) and the supported scope (~30 currencies), which distinguishes it from narrower siblings like fx_dkk.

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?

It gives clear usage context: conversion can be for today or any date in the last 90 days, with fallback to the previous ECB business day. It does not explicitly name alternatives such as fx_dkk or state when not to use this tool, so it falls short of full routing guidance.

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