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Overview

Lookalike Search ranks companies by similarity to a reference company from the same Extruct index used by Semantic Search. It takes a company domain or UUID as input and blends what a company does, who it sells to, firmographics, and traffic into a single ranking.

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This Path Works Best When

  • You trust one company as a good market proxy.
  • You want expansion around a known winner, competitor, or target account.
  • Filters should refine results, but the seed company should drive ranking.

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Choose Another Path If

  • You do not yet have a strong seed company. Start with Semantic Search.
  • You need custom natural-language evaluation criteria instead of index-based similarity. Use Deep Search.

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Prerequisites

export EXTRUCT_API_TOKEN="YOUR_API_TOKEN"
Generate tokens in Dashboard API Tokens. For full setup, see Authentication.

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Endpoints used

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Workflow

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1) Choose company_identifier

company_identifier can be:
  • A domain, for example stripe.com
  • A UUID
If you need a seed company first, use Semantic Search and prefer results[].domain. Use results[].id only if domain is missing. 
COMPANY_IDENTIFIER="stripe.com"

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2) Run lookalike query

curl --get "https://api.extruct.ai/v1/companies/${COMPANY_IDENTIFIER}/similar" \
  -H "Authorization: Bearer ${EXTRUCT_API_TOKEN}" \
  --data-urlencode "offset=0" \
  --data-urlencode "limit=20"

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3) Apply filters if needed

curl --get "https://api.extruct.ai/v1/companies/${COMPANY_IDENTIFIER}/similar" \
  -H "Authorization: Bearer ${EXTRUCT_API_TOKEN}" \
  --data-urlencode 'filters={"include":{"country":["United States"]},"exclude":{"size":["1-10"]}}' \
  --data-urlencode "offset=0" \
  --data-urlencode "limit=20"
For filter rules, use Search Filters Reference.

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4) Page through results

  • Page 1: offset=0&limit=20
  • Page 2: offset=20&limit=20
  • Page 3: offset=40&limit=20

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Choosing a strong seed company

Lookalike quality depends heavily on the seed. Use a company that clearly represents the market you want, not just a well-known brand in the general space. Good seeds:
  • Sell to the same buyer you care about.
  • Have similar company shape or go-to-market motion.
  • Are specific enough that “similar” means something useful.
Weak seeds:
  • Very broad platforms with many unrelated products.
  • Household names that dominate a category but are not representative.
  • Companies that overlap only superficially with your target market.
If you do not trust any single seed, use Semantic Search first or move to Deep Search for explicit criteria.

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Troubleshooting

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401 Unauthorized

The token is missing or invalid. Check that EXTRUCT_API_TOKEN is set and the header is exactly Authorization: Bearer ${EXTRUCT_API_TOKEN}.

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404 Not Found

The reference company is not found in the index. Try another domain/UUID. Reuse a known seed from semantic search (results[].domain or results[].id) to confirm identifier validity.

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422 Unprocessable Entity

The filters JSON is malformed or includes unsupported keys. Validate your filters JSON before sending: echo '<filters-json>' | jq empty.