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

The readOnlyHint annotation already establishes this is a safe read. The description adds the useful behavioral distinction that latest=true is the default and is ignored when a specific invoice is addressed, but says nothing about return format, error cases for non-existent invoices, or cache staleness behavior beyond what the schema already states.

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?

A single sentence that front-loads the operation and then cleanly presents the two retrieval modes in parentheses, followed by the API path. No filler or redundancy.

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 9-parameter read tool with no output schema, the description covers the core mode distinction well, but leaves the agent to infer the return shape, pagination, and error behavior. It is adequate but not rich, and the absence of an output schema shifts some burden onto the description that it does not carry.

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 every parameter is already documented in the schema. The description reinforces the interaction between latest and the date fields, but adds no syntax or format detail beyond what the schema provides. Baseline 3 is appropriate when the schema does the heavy lifting.

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 ('Get a single customer invoice') and explicitly distinguishes the two retrieval modes: the current open invoice via latest=true vs. a specific past invoice via product_plan_id + year + month + day. It also names the underlying API path, and the singular 'single invoice' contrasts cleanly with the sibling amberflo_list_customer_invoices.

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 description clearly names both usage modes and the parameters that select them, so an agent knows when to use latest vs. the date-addressed path. It does not, however, explicitly name amberflo_list_customer_invoices as the alternative for enumerating multiple invoices, leaving that inference to the agent.

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