Live execution cost: what a market order really costs

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

Beyond the readOnlyHint and openWorldHint annotations, the description adds meaningful behavioral details: it covers both sides, uses the full visible order book, explicitly excludes fees, and explains that null means the book cannot absorb that size. This gives the agent a clear picture of edge cases and output interpretation.

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 two front-loaded sentences with no filler. It leads with when to call the tool, then packs scope, content, and edge-case semantics into a compact, highly readable format.

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 fully explains what is returned (cost ladders, basis points, sizes, both sides, 8 perpetuals) and how to interpret null values. This is complete enough for an agent to invoke the tool and understand the result without needing further documentation.

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 tool has zero parameters, so the schema already conveys there is nothing to configure. The description adds useful context about the size range covered ($10K to $5M), aligning with the '0 params = baseline 4' guidance.

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 clearly states the tool's function: it returns live cost ladders in basis points for market order sizes from $10K to $5M across 8 perpetuals. It also distinguishes this from sibling tools by specifying use cases like slippage, book thickness, and thinnest market.

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 description gives explicit invocation guidance ('Call this when the user asks...') and lists three relevant user intents. However, it does not explicitly mention when not to use it or name alternative sibling tools, so it falls just short of a 5.

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