Estimate expected execution price and slippage for a given order size by walking the stored order book, so you can assess trading cost before placing a trade.
Expected execution price and slippage for a size, against the stored book. (alias of slippage)
| Name | Required | Description | Default |
|---|---|---|---|
| side | Yes | ||
| size | Yes | ||
| symbol | Yes | ||
| size_unit | No | ||
| asset_class | No | Which market answers. Inferred from the symbol's source when omitted. |
Changes observed during successful MCP inspections.
v0.3.2Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are supplied, so the description carries the full burden. 'Against the stored book' is a genuine disclosure — the output reflects local book data, not a live venue quote, and presumably no order is transmitted — but nothing states read-only status, staleness risk, permissions, or failure modes when no book is stored. That is thin for an unannotated simulation tool.
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 actual computation and zero preamble or filler. It is tight, though the alias caveat arrives as a trailing parenthetical rather than being integrated into the routing guidance.
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?
Five parameters, no annotations, no output schema, and a nearly undocumenting schema — the description should do more work than two sentences. It never says where the book comes from, how to interpret a stale or missing book, or what shapes the returned price/slippage pair takes.
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 20%; only `asset_class` has an inline description. `side` never documents its accepted values (buy/sell? bid/ask?), `symbol` format is unspecified, and the rambling `$defs` docstring explains `size_unit`'s history rather than what a caller should pass. The description adds nothing beyond 'for a size', so the coverage gap is not compensated.
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 precisely what the call computes — expected execution price and slippage for a given size against the stored book — which is a specific outcome, not a restatement of the name. The parenthetical '(alias of slippage)' identifies the relationship to a sibling, so an agent can tell it duplicates `slippage` rather than complementing it.
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 alias note implies this and `slippage` are interchangeable, which is useful routing information, but it never says which to prefer, whether there is any difference in cost or output, or when not to use it. Usage is implied rather than directed.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.