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

Beyond readOnly/idempotent hints, it discloses that the balance is a snapshot anchored to the last upstream sync, that updateDateTime/updatedAt is the sync instant not a live read, and that rows may degrade to a last-synced balance with realtime:false and a warning under upstream 5xx or non-Open-Finance conditions. It also documents the response shape and structured warnings.

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 front-loaded with the core purpose, then systematically covers snapshot semantics, staleness workflow, parameter constraints, error cases, and response envelope. Every sentence adds distinct value and none are redundant.

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?

With no output schema, the description still tells the agent the result envelope { results, errors } and the key field meanings (updateDateTime/updatedAt, realtime, warning). Despite the tool's complexity, all information needed to call it and interpret edge cases is present.

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?

Even though the schema only says account_ids is a string array, the description adds the required 1–50 element constraint, per-account semantics, and error-response behavior. This fully compensates for the 0% schema description coverage.

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 opening phrase 'Returns the latest available balance per account id' names a specific verb, resource, and scope, and also gives the exact endpoint GET /accounts/:id/balance. It is clearly distinguishable from sibling tools such as openfinance_list_transactions and openfinance_force_sync because it is explicitly a balance read per account.

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 explicitly tells the agent what to do when data is stale or inconsistent: run openfinance_force_sync and re-read if the balance disagrees with the transaction sum. It also explains how to handle credit-specific BALANCE_FETCH_ERROR and BALANCE_CONSENT_ERROR cases, including the fix of reconnecting the bank.

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