Guide - Quoin Data

National property records for Washington, D.C., Maryland and six Northern Virginia jurisdictions (Arlington, Fairfax County, Loudoun, Alexandria, City of Fairfax, Falls Church). Every record carries a citation: publisher, dataset and the date Quoin published it. Base URL: https://portal.quoindata.com/api/v4. Authenticate with Authorization: Bearer <API key> from https://portal.quoindata.com/keys. All operations are GET. Machine-readable schema: /api/v4/openapi.json.

Prices

Operation	Request	Price
`find`	`GET /find?q=&jurisdiction=&types=&limit=`	Free
`catalog`	`GET /catalog?jurisdiction=&source_id=`	Free
`connected`	`GET /entities/{q_id}/connected?depth=`	Free
`records`	`GET /entities/{q_id}/records?kind=&limit=&cursor=`	$0.10
`summary`	`GET /entities/{q_id}/summary?fields=`	$0.10
`history`	`GET /records/{record_ref}/history`	$0.10
`search`	`GET /search?jurisdiction=&kind=&filter=&limit=&cursor=`	$0.10 per page with results

Prices are per successful call. Each page of records or search is a separate call. Errors, empty searches, timeouts, “not found” responses and retries with the same Idempotency-Key are never charged. Welcome credit and billing are shared with v3.

Identifiers

Every entity has a permanent q_id: a type prefix plus a UUID.

Prefix	Entity
`addr_`	Address
`parc_`	Parcel
`acct_`	Tax account
`unit_`	Unit
`juri_`	Jurisdiction (returned in results; not accepted as input)
`rec_`	One source record; all its versions share the id

prop_ (property group) and loan_ are reserved and have no data yet. The entity model differs by state: D.C. has addresses, parcels, accounts and units; Maryland has addresses and accounts; Virginia has addresses and parcels. jurisdiction is one of these Census codes. A county filter on find can take a few seconds; a state filter is fast.

State	Codes	Records	Pulled
D.C.	`11`, `11001`	8.35M	2026-10-08
Maryland	`24`; counties `24001` `24003` `24005` `24009` `24011` `24013` `24015` `24017` `24019` `24021` `24023` `24025` `24027` `24029` `24031` `24033` `24035` `24037` `24039` `24041` `24043` `24045` `24047`, Baltimore City `24510`	43.38M	2026-10-05
Virginia	`51`; Arlington `51013`, Fairfax County `51059`, Loudoun `51107`, Alexandria `51510`, City of Fairfax `51600`, Falls Church `51610`	35.93M	2026-10-12

Typical flow

KEY=qk_...
# 1. Free: resolve an address or parcel/account number
curl -H "Authorization: Bearer $KEY" "https://portal.quoindata.com/api/v4/find?q=1350%20Pennsylvania%20Ave%20NW&jurisdiction=11"
# 2. Free: see what is linked to it
curl -H "Authorization: Bearer $KEY" "https://portal.quoindata.com/api/v4/entities/addr_01a12e0d-2ece-77ad-b5b0-430ab9658f29/connected"
# 3. $0.10: best value per field, each with a citation
curl -H "Authorization: Bearer $KEY" "https://portal.quoindata.com/api/v4/entities/parc_5df9c647-c1fe-6e85-1690-a0710b870cfb/summary"
# 4. $0.10 per page: every cited source record
curl -H "Authorization: Bearer $KEY" -H "Idempotency-Key: $(uuidgen)" "https://portal.quoindata.com/api/v4/entities/addr_01a12e0d-2ece-77ad-b5b0-430ab9658f29/records?limit=50"

Operations

find: q is an address street line (text after the first comma is ignored; exact match after normalizing case and spaces) or an official label (D.C. SSL, Maryland account, Virginia PIN/PARID/RPC). Optional types is a comma list (addr,parc,acct,unit); limit 1–100, default 20. Returns items[] of {q_id, type, label, jurisdiction, matched_on}. No match returns an empty list. catalog: published sources with {state, source_id, source, dataset, kind, records, as_of}. as_of is when the catalog was built, not when the source was pulled (see the table above), and records counts every version. Adding jurisdiction (state level) or source_id also returns fields: each field’s type, fill rate and an example value from a 2,000-row sample. Use these field names in search filters. connected: linked entities up to depth 1–3 (default 2): {q_id, type, relation, via, depth}. Relations: at (at an address), billed_to (account bills parcel), in (in a jurisdiction). records: current source records about the entity and its neighbourhood (depth 2): {record_ref, kind, source_id, jurisdiction, about, published_at, citation, data}. data is the full source row, field names as the publisher wrote them. Optional kind (for example permit, sale, tax, assessment). limit 1–100, default 50. When more exist, data.next_cursor is set; pass it back as cursor. summary: one best value per canonical field: year_built, bedrooms, full_baths, half_baths, living_area_sqft, assessed_total, last_sale_price, last_sale_date. Each item has {field, label, value, citation, record_ref, alternatives}. Optional fields is a comma list. history: every version of one record, newest first: {version, published_at, removed, citation, data}. removed: true means the publisher stopped carrying it. search: records of one kind in one jurisdiction, filtered on the source’s own field names (from catalog): {cursor, record_ref, kind, source_id, jurisdiction, published_at, citation, data, q_ids}. filter is URL-encoded JSON with up to 5 fields; a bare value means eq. Operators: eq, ne, in (list), gt, gte, lt, lte (numbers compare numerically, everything else as text), prefix and contains (3+ characters, no % _ \), exists (true/false). "$source_id" limits the search to one source. limit 1–100, default 50; page with cursor.

# Fairfax County sales of $1M or more
curl -G -H "Authorization: Bearer $KEY" "https://portal.quoindata.com/api/v4/search" --data-urlencode "jurisdiction=51059" --data-urlencode "kind=sale" \
  --data-urlencode 'filter={"$source_id":"fairfax_county_dta_re_sales","PRICE":{"gte":1000000}}'
# Owner lookup: D.C. tax accounts whose owner name starts with SMITH
curl -G -H "Authorization: Bearer $KEY" "https://portal.quoindata.com/api/v4/search" --data-urlencode "jurisdiction=11001" --data-urlencode "kind=account" \
  --data-urlencode 'filter={"ownername":{"prefix":"SMITH"}}'

Searches that match many records return quickly. A filter on a rare value over a large source can run past the time limit; that returns a free 503 query_timeout. Narrow it with "$source_id" or a more common value. Owner names are matched as text, not resolved to people, and a sale’s name fields can hold the seller as well as the buyer.

Response envelope

{"contract_version":"quoin-v4","operation":"records","request_id":"…","status":"ok",
 "data":{"q_id":"addr_…","items":[…],"next_cursor":"…"},"error":null,
 "meta":{"served_at":"2026-10-13T12:00:00.000Z","truncated":false,"next_cursor":"…"}}

Headers: X-Quoin-Price-Micro-USD, X-Quoin-Charged-Micro-USD (0 on replay), X-Quoin-Balance-Micro-USD, X-Quoin-Replayed, X-RateLimit-*.

Errors

Status	`error.code`	Meaning
400	`invalid_request`	Malformed q_id, unknown parameter or jurisdiction, invalid filter, bad cursor
401	`invalid_key`	Missing or revoked key
402	`insufficient_balance`	Credit used up and no saved card
404	`not_found` / `unknown_resource`	Nothing published for that id, no search matches, or no such endpoint
409	`request_id_mismatch`	Idempotency-Key reused for a different request
422	`response_too_large`	Over 256 KiB; lower `limit`
429	`rate_limited`	See `Retry-After`
503	`query_timeout` / `service_unavailable`	Narrow a search, or retry with the same Idempotency-Key. The first call after a few idle minutes can be slow

Limits

Shared with v3, per account: 60 calls per minute, four concurrent, 10,000 free and 1,000 paid calls per rolling 24 hours, and caps on distinct entities delivered per day.

Known data limitations

Some Virginia dates are epoch milliseconds; D.C. sales use 1900-01-01 as a placeholder. summary picks the latest sale by comparing dates as text, so last_sale_price and last_sale_date can come from an older sale. Check alternatives, or read the sale records, when the sale matters.
Maryland has no bedroom or bathroom counts.
catalog filters by state even when given a county code.
Arlington tax payments appear twice (bulk file and API sources, the same rows) until the next Virginia load.
Each source has been published once so far, so history returns one version per record.

​Prices

​Identifiers

​Typical flow

​Operations

​Response envelope

​Errors

​Limits

​Known data limitations