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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds real context beyond that: the computation basis (settled funding applied to today's orientation at your size), the four cost deductions, and the Pro entitlement gate for ranges past 7 days. It does not mention latency, caching, or error behavior, which keeps it below a 5.

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?

A single dense sentence front-loads what is measured, then enumerates the returned metrics and ends with the gating rule. No filler, though the stacked clauses make it slower to parse than a short bulleted framing would be.

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 correctly spends its budget enumerating what comes back: net after four costs, max drawdown, negative days, daily sign flips, and per-exchange history depth. Remaining ambiguity is minor, mainly what 'today's orientation' assumes about direction and whether notional is per side.

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 coverage is 67%, so the schema already carries most of the parameter burden. The description echoes the range set and the 'at your size' notion of notional but adds no format, unit, or constraint detail, and leaves pair_key provenance vague ('from another tool') without naming the tool that supplies it.

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 operation on a specific resource: replay historically settled funding on both legs for one pair, at a given size and range. That is clearly distinct from siblings like funding_rates or pair_breakdown, though no sibling is named explicitly, so differentiation is inferred rather than stated.

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 one concrete guideline is the paywall boundary: 'Ranges beyond 7 days need Pro,' which usefully tells the agent when the call will not be available. There is no guidance on when to pick this over pair_breakdown or funding_rates, so usage context is only implied.

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