get_balance

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

Beyond readOnlyHint=true, the description discloses the currency units, the billing model (proofs past the included plan amount draw from this balance), the failure mode (402 balance_empty when balance is at or below zero), the meaning of billing_enabled, and the exact auth remedy including that start_login will not unlock this tool. This is substantial behavioral context that annotations cannot express.

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-loaded with the purpose, then billing consequences, then a clearly separated ACCESS block. Dense but nearly every clause carries information; the sentence about topping up being dashboard-only could arguably be folded into the access paragraph.

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?

An output schema exists, so return values need not be described, yet the description still pre-empts the key questions: units, what the balance gates, the error condition, and the prerequisite to call it at all. Nothing an agent needs in order to call this correctly is missing.

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?

The tool takes no parameters, so there is nothing to disambiguate; the baseline applies. The description still adds value by naming the units (euro cents and mills) of the primary returned quantity.

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 opens with a specific verb and resource ('Get the prepaid balance') and enumerates the returned fields: balance in euro cents and mills, low-balance threshold, top-up amounts, auto top-up setting. It is clearly distinguishable from list_balance_ledger and get_subscription in substance, but it never names those siblings or explains the boundary explicitly.

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 clear operating context: what consumes the balance, when requests get refused (402 balance_empty), and explicitly rules out top-up/auto-top-up changes ('done by the owner in the dashboard'), which prevents a wasted call. The access prerequisite block is unusually actionable, though it does not say when to prefer this over get_usage or list_balance_ledger.

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