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

Annotations already cover read-only, idempotent, non-destructive, open-world, so the safety profile is settled. The description adds genuinely non-structured behavior: cost ($0.003/call or Carry key) and the default threshold semantics. It does not explain result-set size behavior (the limit parameter) or ordering.

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 definition and threshold, then the routing hint. The "|APR| ≥ min_abs_apr, default 2 = 200 %" clause is dense but decodable; the pricing note earns its place.

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?

For a 2-parameter lookup with no output schema, the description covers the filter and the returned metrics adequately, but the undocumented limit parameter is a real hole for an agent deciding what arguments to pass and how many extremes it will get back.

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 0%, so the description must carry both parameters. It does a good job on min_abs_apr (absolute-value predicate and the "default 2 = 200 %" unit convention) but never mentions limit, leaving result-count behavior undocumented in both places.

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?

States a specific resource and predicate: funding extremes where |APR| >= min_abs_apr, plus the realized 24h/7d/14d averages and hours-in-extreme it returns. It also names the sibling it differs from (carry_aftermath), so an agent can separate it from carry_history/carry_calendar without opening any schema.

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?

"Use for funding extremes with realized averages; for history after extremes use carry_aftermath" gives an explicit use case and routes the adjacent case to a named alternative. It stops short of stating exclusions relative to the other carry_* siblings (breakeven, regime, naked), so it is strong but not exhaustive.

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