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

Annotations already cover read-only, idempotent, non-destructive behavior. The description adds meaningful context: it is a view over existing expenses (paid_to_person_id / income_from_person_id), no parallel ledger table exists, and an API key and cost apply. This helps the agent understand side effects and preconditions. No contradiction with 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?

The description is concise and information-dense: it front-loads the core purpose, then covers lookup, return shape, data provenance, and cost/auth in a few short clauses. It contains no fluff, though mentioning a sibling alternative could have made it even more useful.

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?

Given the read-only annotations and the presence of an output schema, the description does not need to explain return values in detail. It provides data provenance, auth requirements, cost, and the key selection methods. The main gap is unspecified behavior when multiple optional filters are supplied together, but this is minor for an all-optional, read-only 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 input schema covers 100% of parameters with descriptions, including inclusive date filters, default limit, and person_id semantics. The description only restates 'Pass person_id or name' and adds no additional detail about precedence, combination behavior, or format beyond what the schema offers. Baseline 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 identifies a specific function: retrieving a money ledger between the current user and a contact, sourced from expense fields. It also states the lookup key (person_id or name) and the return shape (entries + per-currency totals). However, it does not explicitly distinguish itself from the closely named sibling get_money_between_people, so it is clear but not fully differentiated.

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 context is implied: pass person_id or name, and the tool reuses existing expenses rather than a separate ledger. But it does not name alternatives or explain when to prefer this tool over get_transactions, search_transactions, or get_money_between_people. The when-to-use guidance is present only by inference.

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