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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds substantial non-obvious behavior: balances are never converted between currencies, the positive/negative sign convention, that only friend names are exposed (never emails or avatars), and the empty-result contract. These are exactly the traits an agent cannot get from the annotations.

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 core purpose, then each following clause carries distinct payload: currency rule, sign semantics, privacy constraint, and empty-result handling. No filler or restated title text.

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 carries the return-shape burden and does so thoroughly — itemizing contents, explaining the sign convention, the per-currency scope, and the empty-response path. Nothing an agent needs to call and interpret this tool 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 zero parameters, so per the rubric the baseline is 4. The description adds nothing parameter-related because there is nothing to add — the ledger shape is described instead.

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 states a specific verb and resource — 'Returns the authenticated user's Splits ledger' — and enumerates the exact contents (per-friend balances per currency, totals, groups, 20 recent expenses). That scope distinguishes it from the sibling aggregate tools (get_net_worth, get_budget, get_balance_history) without needing to name them, though no explicit sibling contrast is drawn.

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?

Usage is implied rather than stated: an agent can infer this is the tool for split/shared-expense balances. The empty:true handling is a genuine operational guideline (relay message and next_step_url instead of erroring). But there is no explicit when-to-use versus alternatives, nor prerequisites.

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