list_balance_ledger

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

Annotations already declare readOnlyHint=true and the description does not contradict them. On top of that it discloses ordering (newest first), the sign convention for amounts (signed euro cents, credits positive), and the granularity of usage rows, which are behaviors the annotations cannot convey; the only gap is that pagination/navigation behavior is left entirely to the schema.

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?

Two short blocks: the content/semantics sentence first, then the access precondition. Every clause carries information an agent needs, with no repetition of schema or annotation data.

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-structure explanation is rightly omitted, and the access requirement plus sign convention cover the non-obvious risks. What remains slightly thin is guidance on iterating pages and interpreting the per-month aggregation, but overall it is complete for a read-only list tool.

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%, and both parameters (page, limit) are fully documented with defaults and maxima in the schema itself. The description adds no pagination semantics or format details beyond that, so the baseline of 3 applies.

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 gives a specific verb and resource ('List the prepaid balance history') and enumerates exactly what the rows are: top-ups, refunds, adjustments, and one monthly usage row for deductions. It never names the closely related sibling get_balance (current balance rather than history), so the distinction must be inferred from the word 'history'.

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 states an explicit precondition and recovery path: set PROOF_API_KEY, restart the server, then call again, plus a clear exclusion that start_login does NOT unlock this tool. That is unusually useful routing guidance, but there is no explicit guidance on when to prefer this over get_balance or how to page through large histories.

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