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

With no annotations, the description carries the burden and does well: it discloses the mutation's side effect (ladder advances), a validation ordering rule that can cause rejection, and the return content ('what is due next and when') despite there being no output schema. It omits any mention of permissions or what happens on out-of-order or duplicate submissions.

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?

Three short sentences, front-loaded with the action and effect, then the ordering rule, then the return value. Nothing is redundant or padded.

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 3-parameter mutation with no annotations and no output schema, the description supplies effect, ordering validation, and even the return payload, so an agent can invoke it correctly. Minor gaps remain around error/permission behavior on invalid submissions.

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 'sent' (YYYY-MM-DD, default today), 'stage' (enum 1-3, default lowest unsent) and 'invoice' (id or reference) are already fully documented. The description only broadly restates the date and hints at the stage ordering, adding little beyond the schema — baseline 3.

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+resource (record a chase letter as sent) and its effect (advances the dunning ladder). It is clearly distinguished from the sibling letter_render, which produces the letter rather than recording it.

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?

Establishes the triggering condition (the letter was 'actually sent') and gives an explicit ordering constraint: reminder 2 cannot be recorded before reminder 1. It does not name letter_render or other siblings as the alternative for the 'generate the letter' path, so routing is left partly to inference.

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