Bullrun

Compare funds tracking one index

get_etf_index_group

Read-only

Answer "what is the cheapest way to track ?". Returns every fund tracking one index ordered cheapest fee first, deduplicated to one row per FUND rather than per venue listing (a five-venue UCITS fund is one choice, not five) with its listingCount and venues. Defaults to UCITS-buyable domiciles. Omit indexKey to list the available index families. Fees are percentage points and the response states how many funds publish no fee at all, so a "cheapest" claim is never made over silently omitted funds. Read-only.

Input Schema

Name	Required	Description	Default
`limit`	No	Maximum funds (or index families) to return, 1-100.
`scope`	No	ucits (default) restricts to domiciles a European retail investor can actually buy. all adds US-domiciled trackers, which look cheaper but are not purchasable by EU retail.	ucits
`currency`	No	Keep only funds with a listing trading in this currency (e.g. CHF, EUR, USD, GBP) and name that line.
`exchange`	No	Keep only funds listed on this venue and name each one's ticker there, e.g. SW (SIX Swiss Exchange), XETRA, LSE, AS, MI. A Swiss investor wanting the SIX line passes SW.
`indexKey`	No	Normalized index key, e.g. SP500, MSCI_WORLD, NASDAQ100, MSCI_EM, EURO_STOXX_50, TOPIX, FTSE100. Omit to list every index family that has at least one fund.
`distributionPolicy`	No	Optionally keep only accumulating or only distributing share classes.

Output Schema

Name	Required	Description	Default
`mode`	Yes
`found`	Yes
`funds`	Yes
`scope`	Yes
`webPage`	No
`coverage`	Yes
`indexKey`	Yes
`warnings`	Yes
`platformLink`	No
`indexFamilies`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 19, 2026

addedInput schema / properties / currency

Added value: +{
+  "description": "Keep only funds with a listing trading in this currency (e.g. CHF, EUR, USD, GBP) and name that line.",
+  "type": "string"
+}

addedInput schema / properties / exchange

Added value: +{
+  "description": "Keep only funds listed on this venue and name each one's ticker there, e.g. SW (SIX Swiss Exchange), XETRA, LSE, AS, MI. A Swiss investor wanting the SIX line passes SW.",
+  "type": "string"
+}

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 17, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Goes well beyond the readOnlyHint annotation by disclosing ordering (cheapest fee first), fund-level deduplication, the listingCount/venues payload, the UCITS-by-default scope, and the data-quality caveat that funds with no published fee are counted and named. This is exactly the kind of caveat that prevents an agent from overclaiming "cheapest". Minor gap: no pagination/limit behavior described in prose, though limit is schema-documented.

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-loads the disambiguating question and the core result shape, and every sentence carries information (ordering, dedup, defaults, fee-omission caveat). Some sentences are long and packed with parentheticals, slightly reducing scanability, but there is no filler.

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?

An output schema exists, so return values need not be enumerated; the description still supplies the crucial shape (fund-level rows, listingCount, venues, fee-omission count) and the default scope behavior. Nothing an agent needs to call this correctly or interpret results honestly 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 description coverage is 100%, so the schema already explains limit, scope, currency, exchange, indexKey, and distributionPolicy thoroughly (including the SW example for Swiss investors and the SP500/MSCI_WORLD key format). The description only restates the indexKey-omission behavior and defaults, adding no syntax or semantics the schema lacks. Baseline 3 applies.

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 and resource (returns every fund tracking one index) plus the exact question it answers, and distinguishes itself from listing-level siblings by emphasizing dedup to one row per FUND rather than per venue listing. An agent can tell this apart from compare_etfs, screen_etfs, or get_etf_fund without opening the schema.

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 a clear triggering question ("what is the cheapest way to track <index>?") and the indexKey-omission path for discovery, plus the default scope caveat. It does not explicitly name alternatives such as simulate_etf_cost for total-cost analysis or compare_etfs for multi-fund comparison, so the exclusion guidance is implicit rather than stated.

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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