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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely new behavioral context: the metric is composed of taker fee plus order-book slippage, it covers both perps and spot, and results are ranked cheapest first — all things the annotations cannot convey. It omits data freshness/snapshot timing, which keeps it from 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?

One dense sentence with the metric definition and the result ordering front-loaded; every clause (what is summed, what scope, what sort) earns its place and nothing is padded.

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 read-only computation with no output schema, the description covers what is measured, across which venue types, and how results are ordered. It leaves the return shape (per-venue rows vs. single best) and the default size implicit, a minor gap given the low complexity.

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 only 50% (size_usd has no description), so the description carries weight by clarifying that 'base' is a single coin and that size is a USD notional to be bought or sold. It does not mention the 100k default or the 100–50M bounds, which the schema supplies structurally but without explanation.

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 concrete computed resource (taker fee + order-book slippage) for a specific scope (buy or sell a given USD size of one coin across all perps and spot venues). The 'on every exchange' framing implicitly separates it from venue_execution_cost, but the sibling is never named, 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 phrase 'cheapest first' and 'on every exchange' imply the use case is cross-venue cost comparison before entering a position, but there is no explicit when-to-use, when-not-to-use, or pointer to venue_execution_cost for single-venue queries. Usage is left to inference.

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