List friends

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds real semantic value beyond that: balances are aggregated per currency and the sign convention (positive = friend owes user, negative = user owes friend) is spelled out, which the agent cannot get from any structured field. It does not mention pagination, ordering, or rate limits.

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 sentences, front-loaded with the purpose and followed by the one piece of interpretation guidance an agent actually needs. Every sentence earns its place with no filler or restatement of the title.

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?

There is no output schema, so the description is the only source of return-value information, and it covers only the balance figures and their sign. It says nothing about the other likely fields (friend id, name, email) that an agent would need to chain into create_expense or settle_up, leaving a meaningful gap for a zero-parameter listing 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?

The tool takes zero parameters, which is the baseline-4 case; there is nothing for the description to disambiguate. The description does not waste space re-explaining schema details and instead spends its words on output semantics.

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+resource ("Lists the user's Splitwise friends") and names the payload (overall balance per currency), which clearly separates it from siblings like list_groups, list_expenses, and settle_up. It stops short of the 5 mark because it never distinguishes itself from get_balances, which plausibly overlaps on balance data.

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 only implied: an agent can infer this is the way to enumerate friends and obtain their balances, but the description never says when to prefer it over get_balances or when friend data is a prerequisite for other calls. No exclusions or alternatives are named, so routing depends on inference from the tool name.

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