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

With no annotations provided, the description carries the full burden. It discloses that the tool returns the converted amount and rate, uses live mid-market rates, and does not support crypto pairs. However, it does not specify the exact rate provider (only mentions ECB/Frankfurter as not specifically needed) or any potential rate latency limits, leaving some ambiguity about the data source.

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 front-loaded with the core purpose in the first sentence, followed by structured usage guidance and exclusions. Every sentence contributes value, making the length justified given the large sibling list. There is no redundancy or filler.

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?

The description covers the essential aspects: function, output fields, usage context, exclusions, and supported currency codes. It would be more complete if it mentioned the rate source explicitly or potential error conditions, but for a lite conversion tool with no output schema, it provides sufficient context for an agent to select and invoke 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% with all three parameters (amount, from, to) having descriptions. The description adds minimal extra value beyond the schema, such as accepting 'all major ISO 4217 currency codes' and confirming amount must be positive. It does not provide syntax or formatting details beyond what the schema already includes.

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 clearly states the tool's function: 'Converts a foreign exchange (FX) amount between two fiat currencies using live mid-market rates. Returns the converted amount and the exchange rate applied.' It also explicitly distinguishes from sibling tools by naming them and their purposes, such as 'currency_convert' for richer metadata and 'currency_rates' for historical rates.

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?

The description provides explicit usage guidance: 'Use currency_fx_lite when only the numeric result is required and the ECB/Frankfurter data source is not specifically needed.' It also gives clear alternatives for other scenarios (prefer currency_convert, currency_convert_lite, currency_rates, currency_convert_open) and explicitly excludes crypto pairs, directing users to crypto_fx_rates or crypto_price_lite.

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