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

Annotations only carry destructiveHint=true, but the description adds crucial context beyond that: the operation is PERMANENT, invoices cannot be changed or deleted, and an invoice number is consumed. It also discloses side-effect scope (not emailed, not booked, no direct debit), which an agent cannot infer from the annotation alone.

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-loads the purpose, then the irreversibility warning, then prerequisites, then the return value. Every sentence carries information an agent needs, with no filler.

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?

Despite having no output schema, the description states the return value (new id and invoice number) and covers the mutation's irreversibility and side effects. For a 9-parameter write tool this is complete enough to invoke safely.

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 the baseline is 3. The description reinforces the required fields and points to eboekhouden_list_invoice_templates for template_id, but adds little syntax or format detail beyond what the schema already documents for all 9 parameters.

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 ('Create a sales invoice for a relation') and clearly distinguishes itself from siblings like eboekhouden_get_invoice and eboekhouden_list_invoices. The scope is unambiguous 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?

Gives concrete prerequisites (relation_id, template_id, term_of_payment, at least one item with ledger_id) and explicitly scopes out adjacent behaviors ('NOT e-mailed', 'NOT booked as a mutation', 'no direct debit'). It does not name a competing sibling or a when-not-to-use alternative, so it falls short of a 5.

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