> ## Documentation Index
> Fetch the complete documentation index at: https://docs.focusalpha.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Screen ETFs by Asset Class

> Filter the US-listed ETF universe by the four-level holdings taxonomy — asset_class, category, segment, specializations — or by a dotted-path taxonomy_prefix.

Screening ETFs by asset class uses the [four-level holdings taxonomy](/etf/taxonomy) as the filter vocabulary: `asset_class` at level 1, `category` at level 2, `segment` at level 3 (the peer-group key), and `specializations` at level 4. Because the labels are computed from holdings rather than fund names, a screen on these codes returns funds by what they actually hold.

<Info>
  **Plan:** Fund · **Credits:** 1 per call; screen facets and the taxonomy endpoint are free
</Info>

## The Asset-Class Filters on the ETF Screen

<ParamField query="asset_class" type="string">
  Comma-separated level-1 codes; matches ANY. The values are `equity`, `fixed_income`, `multi_asset`, `commodity`, `crypto`, `currency`, `volatility`.
</ParamField>

<ParamField query="category" type="string">
  Comma-separated level-2 codes, e.g. `equity.sector`, `equity.size_style`, `equity.thematic`, `fixed_income.corporate`, `fixed_income.municipal`, `multi_asset.allocation`, `crypto.futures`. There are 38 categories; the free taxonomy endpoint lists them all.
</ParamField>

<ParamField query="segment" type="string">
  Comma-separated level-3 codes — **the peer-group key**, e.g. `equity.sector.health_care`, `fixed_income.corporate.high_yield`, `equity.size_style.emerging`, `equity.leveraged_inverse.single_stock`.
</ParamField>

<ParamField query="specializations" type="string">
  Comma-separated level-4 codes; matches funds carrying **any** of them — the only multi-valued level, e.g. `equity.sector.health_care.biotechnology`, `equity.thematic.ai_robotics`.
</ParamField>

<ParamField query="taxonomy_prefix" type="string">
  A dotted-path prefix matching any level: `equity.sector` is every sector fund, `fixed_income` is every bond fund, `equity.leveraged_inverse` is every leveraged equity fund.
</ParamField>

## Codes Are Exact — an Empty Page Means a Misspelling

The taxonomy codes cannot be guessed, and a misspelled code returns an empty page rather than an error — which reads exactly like "no such funds exist". Retrieve the vocabulary from the free [taxonomy endpoint](/etf/taxonomy), or call the free screen facets endpoint, which returns the codes **as actually carried by funds** with a count for each.

## Labels Answer "What Is It", Not "How Big Is the Position"

A taxonomy filter selects funds whose book **concentrates** in that node under the stated per-node rules. To bound the actual measured share of something — US weight, large-cap weight, treasury weight — combine the label filter with the measured filters documented on [Screen ETFs by Portfolio Shape](/screening/etf/by-portfolio-shape) and [by Geography](/screening/etf/by-geography). "Large-cap biotech" is a segment plus a specialization plus a measured floor, because sector funds carry no cap-band label.

## Related Screens

[By geography](/screening/etf/by-geography) · [By wrapper and structure](/screening/etf/by-wrapper) · [By size and fees](/screening/etf/by-size-and-fees) · [By portfolio shape](/screening/etf/by-portfolio-shape) · [By flows and premium](/screening/etf/by-flows-and-premium) · [ETF screening overview](/etf/screening)

<RequestExample>
  ```bash cURL theme={null}
  curl "https://api.focusalpha.ai/v1/etfs/screen?segment=equity.sector.health_care&sort=aum" \
    -H "Authorization: Bearer $FOCUSALPHA_API_KEY"
  ```
</RequestExample>

<ResponseExample>
  ```json Response (XLV, fields trimmed) theme={null}
  {
    "data": [
      {
        "ticker": "XLV",
        "name": "State Street Health Care Select Sector SPDR ETF",
        "tier": "plain_beta",
        "asset_class": "equity",
        "category": "equity.sector",
        "segment": "equity.sector.health_care",
        "specializations": [
          "equity.sector.geo_us",
          "equity.sector.health_care.drug_manufacturers_general"
        ],
        "aum": 43909783508.08,
        "net_expense_ratio": 0.0008
      }
    ]
  }
  ```
</ResponseExample>