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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety is covered. The description adds genuine behavioral detail beyond that: it discloses that forward_rates_basis can be empty 'with the reason stated when no feed supplies a forward curve', and that it reports missing spot rates and placeholder booking rates, which tells the agent how to interpret edge-case output.

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?

Three sentences, front-loaded with the resource and its payload, then the usage trigger, then supplementary fields. The middle sentence is long and list-heavy, but every clause carries concrete content rather than 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?

With an output schema present, the description need not explain return values, yet it still orients the agent on the most consequential edge cases (missing rates, empty forward basis, unsupported currencies). For a parameterless read tool of this breadth, nothing an agent needs to invoke or interpret it is missing.

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?

Zero parameters, so there is nothing for the description to disambiguate; the baseline of 4 applies. The schema also confirms 'No inputs', reinforcing that no argument semantics are needed.

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 names a specific resource (rate assumptions) and enumerates its contents concretely: spot rates, source labels, timestamps, override presence, missing rates, invoice rows, market convention, forward rates with basis, and unsupported currencies. This is clearly distinguishable from siblings like get_data_quality or get_market_regime 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?

It gives an explicit usage trigger: 'Use when users ask where a number came from or why a rate/P&L is unavailable.' That is a clear context, but it names no alternative tool for adjacent questions (e.g. general data quality), so it stops short of full when-not/alternative routing.

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