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

Annotations already declare readOnlyHint=true, so 'this tool only reads: it never marks a payment as processed' largely restates the annotation, though the specific reassurance about not changing processing state is mild added value. The description adds the backing endpoint (GET /invoices/payment_list?processed=) for traceability but says nothing about result size, ordering, or pagination.

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 short sentences, front-loaded with the scope and immediately followed by the read-only guarantee. The endpoint line is arguably low-value for an agent but is compact and harmless.

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 one-parameter read tool whose annotations already cover the safety profile, the description covers invocation but there is no output schema and no statement of what a returned payment record contains (fields, ordering, volume), leaving a real gap for an agent planning to consume results.

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% and the single 'processed' parameter documents its own yyyy-MM-ddTHH:mm format and pattern. The description's 'after a time stamp' adds the comparison semantics but no format or edge-case detail beyond the schema, so baseline 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?

Names a specific verb and resource ('List incoming invoice payments') and narrows the scope to payments 'not marked as processed' after a timestamp, which distinguishes it from the unfiltered sibling runmyaccounts_list_invoice_payments. It does not explicitly call out that sibling, so the differentiation is inferable rather than stated.

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 phrase 'not marked as processed after a time stamp' implies the reconciliation/bookkeeping use case, but there is no explicit 'use this when...' guidance and no named alternative (the sibling list_invoice_payments is never mentioned). Usage must be inferred from the scope clause.

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