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

Beyond the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false), the description discloses several traits the annotations cannot convey: the per-call confirmation default and how to disable it, that the action reaches a real person and should be user-confirmed, the API key requirement, and the specific error condition for contacts without an email. This is unusually rich operational context.

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 core action and its two modes are front-loaded, and each sentence carries information. There is mild redundancy in the confirmation guidance ('By default you confirm each call' and 'confirm with the user before each call'), but the overall structure is efficient.

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 two-parameter, no-output-schema tool, the description covers the prerequisite, the mode-dependent behavior, the download return value, error conditions, and auth needs. Nothing critical is missing, though the mode-dependent return shape for email sends is left implicit.

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%, so the schema already documents both params, but the description adds genuine meaning: it explains that 'download' returns the file and sends nothing, and that 'email' routes to the contact's address and can fail. That is more than the schema's terse enum description provides.

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 description names a specific verb and resource ('Send a posted invoice') and clearly distinguishes its two modes: emailing the customer or retrieving the file as a download. It stops short of explicitly naming the sibling it replaces (e.g., odoo_post_invoice to post first, or odoo_get_invoice for retrieval), so sibling differentiation is implied rather than stated.

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?

It gives concrete usage conditions: email vs. download mode semantics, the prerequisite that only posted invoices can be sent, and the failure mode when no contact email exists. This is solid when-to-use context, but it never names an alternative tool (e.g., post or fetch an invoice) for the cases where this tool is the wrong choice.

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