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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds value beyond that by detailing the returned contents (including payments only for invoices) and stating the auth requirement ('Needs the user's Cotlet API key with access to this app'). That is meaningful context the structured fields do not carry.

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 opening clause ('Full estimate or invoice: client, line items, tax, discount, deposit and the payments recorded') is nearly restated verbatim in the next sentence, so a sentence of budget is spent on duplication. Purpose is front-loaded, but the redundancy keeps it from being tight.

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 must convey return values, and it does list them (client, line items, tax, discount, deposit, payments). Combined with the auth requirement and the pre-send usage note, an agent has enough to call it correctly, though the return detail is somewhat duplicated rather than expanded.

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 schema already says document_id comes from list_estimates or list_invoices, which is essentially what appears in the description. The description adds no syntax or format beyond that, 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 (get) and resource (a single estimate or invoice) and enumerates exactly what is returned: client, line items, tax, discount, deposit, payments. This clearly separates it from sibling list tools (joist_list_estimates, joist_list_invoices) and mutation tools (joist_send_document, joist_convert_estimate_to_invoice).

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?

Provides an explicit usage condition: 'Use it before changing or sending a document so your agent sees what the client will see.' That tells the agent a concrete pre-mutation checkpoint. It doesn't explicitly name the alternative list tools that produce the document_id, so it stops short of full when/when-not routing.

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