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

No annotations are provided, so the description carries the full disclosure burden for a mutation tool and largely drops it: nothing about required permissions/ownership, reversibility, idempotency, or what happens when the request is already expired or closed. The parenthetical '(default extension window in days)' is also misleading, since the schema makes expiryDays a required argument rather than an optional default.

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?

It is a single front-loaded sentence with the verb and resource in the first three words and no filler. It is efficient but so sparse that the brevity shades into under-specification rather than disciplined concision.

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 two-parameter mutation with no annotations and no output schema, the definition should at minimum clarify the idOrPid identifier form, state the open-request precondition, and hint at the success/error outcome. None of that is present, leaving the agent with real uncertainty before invocation.

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 only 50%: expiryDays is documented in the schema (1-365), but idOrPid has no description anywhere, and the description does not explain that it accepts either a request ID or a payment ID. Instead of filling that gap, the description adds an ambiguous 'default extension window' phrase that has no schema counterpart.

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 pairs a specific verb (extend) with a specific resource (payment request expiry) and constrains it to open requests, which is enough to separate it from siblings such as cancel_payment_request and create_payment_request. It stops short of naming an alternative explicitly, so it lands at 4 rather than 5.

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 'open' implies a precondition (only non-expired, still-active requests can be extended), but the description never states that as a rule, nor does it mention who may extend, whether an already-expired request can be revived, or which sibling to use instead for cancellation or lookup. Usage is inferable but not spelled out.

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