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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=true, so the write/non-destructive profile is covered. The description adds genuinely new context: notes are internal and 'nothing is sent' to the customer, which is a real side-effect disclosure beyond the annotations, plus the underlying POST /notes transport. It stops short of stating permissions or idempotency behavior in prose.

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 operation type and free of filler. The trailing 'POST /notes' is mildly redundant with the tool name but useful transport context; overall the size is well matched to a simple write tool.

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 three-parameter write tool with no output schema and full schema coverage, the description covers purpose, target selection, and the key side-effect boundary (nothing is sent externally). It could add permission or duplicate-note behavior, but nothing essential for correct invocation 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 description coverage is 100%, so the baseline is 3, but the description adds a constraint the schema does not express: exactly one of invoice_id or customer_id must be supplied. The schema marks only 'notes' as required and does not enforce an either/or, so this sentence carries real semantic weight.

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 ('add an internal note') plus both allowable targets ('to a customer or an invoice'), and the 'WRITE:' prefix immediately separates it from read siblings like invoiced_list_notes. An agent can pick this over the list/get note tools without opening any 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?

The description establishes context (internal notes on a customer or invoice) and the 'give exactly one' targeting rule, so usage is implied. However, it names no alternative tool and gives no when-not guidance, leaving an agent to infer that this tool and not invoiced_list_notes is the right call for creating a note.

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