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

Annotations declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is already covered. The description still adds real context beyond that: it enumerates the returned surface, notes the public link can be null, and warns that the name typed by a client answering from the link is client-authored text — a meaningful trust caveat for an agent.

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?

The verb and resource are front-loaded in the first clause, and the long field enumeration is justified because no output schema exists to convey return shape. The sentence is run-on and the field list could be grouped, but no sentence is wasted.

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?

With no output schema, the description carries the return-value burden and does so thoroughly, including the estimate/invoice cross-reference and the client-authored name note. It omits error behavior for an invalid ID and does not point to list_invoices, which a read-only fetch of this complexity would ideally include.

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 parameter's schema text ('The invoice or estimate.') already defines its meaning. The description merely restates that the target is an invoice or estimate, adding no format, ID-source, or ambiguity guidance. Baseline 3 applies when the schema does the work.

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 opening clause states a specific verb and resource ('Reads one invoice or estimate in full'), which immediately separates it from mutating siblings like update_invoice and from the collection tool list_invoices. An agent can select it without opening the 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?

There is no when-to-use or when-not-to-use guidance and no mention of alternatives such as list_invoices to discover an ID. The description never explains how an agent should obtain a valid invoiceId or what distinguishes this fetch from get_invoice_email_draft.

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