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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavioral context – that output carries an inbound_processing_note for restricted currencies and that hold durations are explicitly not in the data – but it does not describe the shape of the session/liquidity windows returned beyond naming them. Solid additive context on top of annotations, not exhaustive.

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 purpose then bullets the two usage modes; the caveat block is long but every sentence carries a real instruction (what not to say, which tool to call instead). The trailing Examples block is somewhat redundant with the schema's ordering semantics, keeping it just short of maximal.

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?

An output schema exists, so return values need no explanation, and the description covers purpose, both call modes, the safety caveat, the escalation path to country_banking_rules, and the inbound_processing_note. Nothing an agent needs to invoke or interpret this correctly 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?

Schema coverage is 100% and the single optional parameter is already documented, so the baseline is 3. The description goes slightly beyond by spelling out the two call modes' outcomes ('optimal window' when passing a code vs 'all market sessions and overlap windows' when omitting) and gives concrete examples (EUR, JPY, INR).

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 and resource ('Get FX trading windows... Returns market sessions and liquidity windows for a currency') and clearly differentiates itself from siblings like fx_rate, fx_volatility, and payment_cutoff_times by scoping to session/liquidity timing. An agent can route to it without opening the 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?

Explicitly names the primary reliable use (rate/spread optimization) and a use-with-care case (delay diagnosis), then redirects to a named alternative (country_banking_rules(destination)) for the binding delivery-side cutoff. It also tells the agent what not to claim ('held until the next session', quoted hold durations) – a rare and valuable negative constraint.

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