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

Annotations already declare readOnlyHint=true, and 'READ ONLY — does not create or approve payments' largely restates that safety profile rather than adding new behavioral context. The GET /payment_orders endpoint reference is metadata, not behavior; pagination semantics (cursor-driven paging) are left entirely to the schema.

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?

Extremely short and front-loaded: the operation and its scope are stated in the first clause with no wasted words. The trailing 'API: GET /payment_orders' is arguably decorative for an agent that already has the tool name and annotations, costing it the top mark.

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 zero-required-parameter read-only list tool with full schema coverage and no output schema, an agent has everything needed to invoke it correctly. Only the pagination flow (using next_cursor from a prior response) is implicit and would benefit from a sentence.

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 100%, so all five filters (status, per_page, direction, after_cursor, counterparty_id) are already documented with meaning in the schema. The description adds no filter semantics of its own, so the baseline of 3 applies.

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+resource ('List payment orders') that is immediately distinguishable from the singular sibling modern_treasury_get_payment_order. However, it never explicitly contrasts itself with get_payment_order or the other list_* siblings, so differentiation relies on the agent's reading of the name alone.

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?

There is no statement of when to use this tool versus the many sibling list tools (list_transactions, list_returns, list_expected_payments) or versus get_payment_order for a single record. The parenthetical about being read-only constrains scope but is not usage routing.

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