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

Annotations only declare readOnlyHint and openWorldHint, so the description must carry most of the behavioral load. It does add meaningful context beyond annotations: the live order book basis for slippage, the 28-venue scope, and that every figure carries a timestamp and source, which signals data freshness and provenance. It stops short of describing the response shape or how ties/ranking are presented.

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 core purpose is front-loaded in a single dense sentence followed by a short scope/provenance clause. It is efficient with no filler, though the parenthetical venue list is slightly long for the value it adds.

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 does enough for a low-complexity read tool: it explains the computation, the venue universe, and that figures are timestamped and sourced. What is missing is whether the response is a single winner or a ranked comparison across venues.

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 100%, so all three parameters are already documented in the schema, giving a baseline of 3. The description reinforces that size is a market-order notional and implies fee-tier sensitivity, but adds no parameter-level detail beyond the schema (e.g., how monthly_volume_usd changes the ranking).

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 opens with a precise verb+resource question ("Which decentralised perpetual exchange is cheapest right now to open and close a market order of a given size") and enumerates the cost components (taker fees on both legs plus real slippage) and coverage (28 perp DEXs, named examples). This clearly separates it from siblings like trading_cost, cost_per_point, and execution_plan.

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 by "cheapest right now" for a market order of a given size, which tells the agent this is a live cost-comparison lookup. However, it never states when to prefer it over siblings such as trading_cost or execution_plan, nor any exclusions or prerequisites.

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