Hopi

Position size calculator

hopi_position_size_calculator

Read-onlyIdempotent

Work out how large a position to take so that hitting the stop-loss loses only a chosen percentage of the account. Enter account size, risk percentage, entry price and stop-loss price. Returns units to buy, position value, amount at risk and stop distance. Figures are treated as GBP. Source: https://hopi.co.uk/position-size-calculator/

Input Schema

TableJSON Schema

Name	Required	Description
`risk`	Yes	Percentage of the account to risk on this trade (above 0, up to 100)
`stop`	Yes	Stop-loss price per unit
`entry`	Yes	Entry price per unit
`account`	Yes	Total account size

Output Schema

TableJSON Schema

Name	Required	Description
`note`	No
`units`	No
`summary`	Yes
`direction`	No
`source_url`	Yes	The tool's page on hopi.co.uk (cite or open to check the figure)
`unitsString`	No
`amountAtRisk`	No
`positionValue`	No
`amountAtRiskString`	No
`positionValueString`	No
`stopDistancePercent`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 20, 2026
- addedOutput schema / required
```
Added value: +[
+  "source_url",
+  "summary"
+]
```
First observedSep 20, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already declare this as read-only, idempotent, and non-destructive, and the description adds useful behavioral details: it lists the return outputs (units, position value, amount at risk, stop distance) and discloses the GBP currency assumption. This gives the agent a clear picture of what the tool computes and returns beyond the structured annotations.

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

Conciseness5/5

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

The description is compact and front-loaded: first sentence states the purpose, second lists inputs, third lists outputs, and the final one notes currency and source. Every sentence adds relevant information, and there is no filler or redundancy.

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

Completeness5/5

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

For a simple calculator with four fully documented parameters, read-only annotations, and an output schema, the description covers purpose, required inputs, output values, currency assumption, and source. Nothing essential for correct invocation is missing.

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

Parameters3/5

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

Schema coverage is 100%, so the schema already documents all four parameters with clear meanings. The description restates the inputs in plain language, which is helpful but not additive, and adds the GBP currency context. This meets the baseline without significantly expanding on the schema.

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?

The description uses a specific, outcome-oriented verb ('Work out how large a position to take') and states the exact resource and purpose: position sizing based on stop-loss risk. It is clearly distinguishable from sibling calculators by explaining the risk-based calculation rather than just naming the tool.

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

Usage Guidelines4/5

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

The description gives clear context for when to use the tool: when you know account size, risk percentage, entry price, and stop-loss price and want to size a position accordingly. It does not explicitly mention alternatives or exclusions, but the described use case is unambiguous enough for an agent to select it over sibling calculators.

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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