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by io.github.kburrus64-max
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Position Size Calculator

position_size
Read-onlyIdempotent

FREE, no key. Position-size / risk calculator: account size, risk %, stop distance and point value -> risk amount, size rounded down to your lot step (optional max size cap) and actual risk. Informational only, not financial advice.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "account_size": "<account_size>",
      "risk_pct": "<risk_pct>",
      "stop_distance": "<stop_distance>",
      "point_value": "<point_value>"
    },
    "name": "position_size"
  }
}

Input Schema

NameRequiredDescriptionDefault
lot_stepNosize increment, default 0.01
max_sizeNooptional cap on size (broker/prop-firm limit)
risk_pctYespercent of account to risk on this trade, e.g. 1
point_valueYesvalue of 1 unit of size per 1 price point, in account currency
account_sizeYesaccount equity in your account currency
stop_distanceYesdistance from entry to stop, in price points

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4.1/5.0
Behavior4/5

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

Annotations already declare readOnly, idempotent and non-destructive, so the safety profile is covered. The description still adds real behavioral context: no API key required, output is rounded down to the lot step, an optional max-size cap is applied, and the result is informational rather than actionable advice.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the useful qualifier 'FREE, no key', then a single dense sentence describing the computation via arrows. It stays short and packs a lot in, though the arrow notation makes it slightly harder to scan than clean prose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description carries the return-value burden and does it well, naming the three returned values (risk amount, size, actual risk). It omits edge-case/error behavior, which keeps it just short of complete for a six-parameter financial calculator.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3. The description earns an extra point by describing output-side semantics not in the schema: rounding down to the lot step and the optional max-size cap, which tell the caller how lot_step and max_size actually behave.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource ('Position-size / risk calculator') and enumerates exactly what inputs go in (account size, risk %, stop distance, point value) and what comes out (risk amount, lot-stepped size, actual risk). This is clearly distinguishable from generic siblings like 'calculate' or 'unit_convert'.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when this is useful (sizing a trade from account/risk/stop inputs) and notes it is 'Informational only, not financial advice', but it never states when to prefer it over the related 'calculate' or 'prop_firm_rules' siblings, nor does it name prerequisites or exclusions. Usage is inferable but not guided.

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

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