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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces this ('It changes nothing; correcting and resending are separate steps') while also disclosing an auth requirement ('Needs the user's Cotlet API key with access to this app') — genuine added context. It does not cover pagination or error behavior, but for a scoped read this is solid.

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?

Front-loaded with the purpose, then return contents, then the non-mutating note, then auth. Four efficient sentences with no filler; the auth line leans slightly boilerplate but is operationally useful.

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 correctly enumerates the return fields (reason text, error code, rejection date), states the safety profile, and covers the auth prerequisite. For a simple single-entity read it is essentially complete, missing only error/not-found handling.

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 both company_id and invoice_id are already documented in the schema (invoice_id even cites list_invoices/create_invoice as its source). The description adds no format or syntax detail 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 and resource ('Get the reason SDI rejected an e-invoice') and even names what it returns (reason text, SDI error code, rejection date). It is clear on its own, but it does not explicitly contrast itself with nearby siblings like get_einvoice_status or verify_einvoice, so it stops short of the sibling-differentiating 5.

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 'for an invoice that SDI discarded' scopes the scenario, and 'correcting and resending are separate steps' steers the agent away from expecting remediation here. However, no alternative tool is named and no when-not-to-use condition is stated, so usage is only implied.

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