Bullrun

Simulate ETF cost

simulate_etf_cost

Read-only

Simulate expense-ratio, assumed bid/ask spread, commissions, and recurring contributions over a holding period. Compares the same gross-return path with and without costs and reports direct charges plus ending-value drag. Taxes, FX, market impact and brokerage-specific fees are excluded unless represented by the inputs. Read-only.

Input Schema

Name	Required	Description	Default
`years`	No
`ticker`	Yes	Exact Bullrun ETF listing ticker.
`spreadPct`	No	Assumed full bid/ask spread in percentage points; each purchase pays half the spread.
`expenseRatioPct`	No	Optional expense-ratio override in percentage points. Otherwise uses the stored ETF profile value.
`initialInvestment`	No
`commissionPerTrade`	No
`contributionAmount`	No
`grossAnnualReturnPct`	No	Assumed annual return before ETF and trading costs, in percentage points. Default 0 isolates direct costs.
`contributionFrequency`	No		monthly

Output Schema

Name	Required	Description	Default
`ticker`	Yes
`results`	Yes
`webPage`	No
`warnings`	Yes
`assumptions`	Yes
`platformLink`	No
`costBreakdown`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 12, 2026

addedOutput schema / properties / platformLink

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "description": {
+      "type": "string"
+    },
+    "label": {
+      "type": "string"
+    },
+    "url": {
+      "format": "uri",
+      "type": "string"
+    }
+  },
+  "required": [
+    "label",
+    "url",
+    "description"
+  ],
+  "type": "object"
+}

addedOutput schema / properties / webPage

Added value: +{
+  "format": "uri",
+  "type": "string"
+}

AddedAug 11, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the trailing 'Read-only' adds nothing. However the description does disclose real behavioral content beyond annotations: the exclusions list and the fact that the output reports direct charges plus ending-value drag, telling an agent this is a deterministic no-side-effect what-if model.

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 core action, and the exclusion sentence earns its place by preventing misuse of the results. The standalone 'Read-only.' fragment is pure duplication of the readOnlyHint annotation and is the one wasted element.

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 an output schema present and annotations covering the safety profile, the description need not explain return values, and it goes further by summarizing what the report contains. It is nearly complete for a 9-parameter simulation tool; only the required ticker and default initialInvestment go unmentioned.

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 description coverage is only 44% across 9 parameters, so the description must carry weight; it does name the cost categories (expense ratio, spread, commissions, contributions, holding period) that map to those inputs, but adds no format, unit, or default detail beyond what the schema already states. The required ticker and initialInvestment are never addressed.

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 (simulate) and a specific resource (ETF cost: expense ratio, spread, commissions, contributions) and describes the comparison method (same gross-return path with and without costs). No sibling tool does simulation, so it is unambiguous against the surrounding screen_etfs/get_etf_* family.

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?

Gives clear scope boundaries — what the model does and does not include (taxes, FX, market impact, brokerage-specific fees) — which tells an agent when this tool's answer is and isn't applicable. It never explicitly names an alternative or states a 'use this instead of X' condition, so it stops 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.

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