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

The description adds behavioral context beyond annotations, such as error behavior ('Errors clearly when no default payment method is on file, or when the requested amount... falls outside the allowed range') and the fact that re-running clears previous failed state. Annotations are all false and are consistent.

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 description is concise at three sentences, with the main action front-loaded. Every sentence adds value (prerequisite, error handling, retry behavior) without 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?

Given the tool's complexity (3 parameters with defaults, prerequisite, error cases) and the presence of an output schema, the description is complete. It covers necessary context for the agent to use the tool correctly.

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 mentions the parameter types (amount, threshold, monthly cap) but does not add new meaning beyond what the schema 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 clearly states the main action: 'Turn on automatic credit top-ups and set (or update) their terms.' It uses a specific verb ('turn on and set/update') and resource ('automatic credit top-ups'), and distinguishes from siblings like disable_auto_top_up and purchase_credits.

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 provides usage guidance by stating a prerequisite: 'Requires a default payment method already on file (a manual credit purchase saves one).' It also explains that re-running clears failed state, acting as a retry. While it doesn't explicitly say when not to use it, the context of sibling tools implies its purpose.

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