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

Annotations already cover readOnly, idempotent, closed-world and non-destructive, so the bar is lower. The description still adds material context the annotations cannot: the required credential scope and the 403 refusal for self-registered sandbox keys, which is exactly the kind of precondition an agent needs before calling.

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 what is read and what comes back, followed by the two access prerequisites. Nothing is redundant with the annotations or schema.

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 single-parameter read tool with no output schema, the description covers the operation, the returned fields, the credential scope, and the workspace-claim precondition. An agent has everything needed to call it and to interpret a 403.

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 100% and the schema itself explains that invoice_id is the UUID from a list_invoices result. The description mentions only that one invoice is read and adds nothing about the identifier's format or source, so the 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?

States a specific verb and resource ("Read one invoice") and enumerates the fields returned (customer, number, status, amount, currency, due date), which implicitly separates it from list_invoices and update_invoice. It never names a sibling explicitly, so an agent must infer the single-vs-list distinction from the word "one".

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?

Gives concrete preconditions: a Last Price credential with billing read scope and a claimed workspace, with the specific failure mode (403) when unclaimed. It stops short of stating when to prefer this over list_invoices or how to obtain the invoice_id beyond the schema note.

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