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

Annotations already declare write (readOnlyHint=false), idempotent, and non-destructive, but the description adds a non-obvious financial guarantee: creating the session does not charge the buyer. That is real value beyond the structured fields. It stops short of explaining auth requirements or what happens after checkout completes.

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?

Two tight sentences with zero waste; the create/resume scoping comes first and the no-charge caveat follows. Nothing is repeated from the schema or annotations.

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 one parameter at full coverage and an output schema handling return values, the description covers what an agent needs to invoke the tool safely, including the no-charge nuance. The missing piece is guidance on choosing this over the other funding siblings.

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?

Only one parameter, fully documented at 100% schema coverage, so the baseline is 3. The description's phrase 'external Trade order' loosely reinforces the meaning of order_id but adds no format, source, or validation detail beyond the schema.

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 pair (create or resume) and a concrete resource (Stripe Checkout session) scoped to external Trade orders. This is clearly distinguishable from siblings like nexus_trade_create_payment_intent and nexus_trade_prepare_funding, which imply a different funding mechanism.

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 word 'resume' hints at the reuse case and the description implies this is the handoff to Stripe Checkout, but no alternatives (e.g. prepare_funding vs payment_intent vs checkout) are named and no when-not condition is given. Usage is implied rather than stated.

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