API Reference

The Fía Rent API returns an estimated fair monthly rent for any US address — blending Census median rent with Fía comparables, plus an AI market read on paid plans.

Base URL & authentication

Base URL https://fia.rent. Every request needs your key in the x-api-key header — create one at /developers/keys.

Keys & quota

• Your monthly quota belongs to your account and is shared across all your keys.
• Create multiple keys (dev / prod / rotation) — they're just credentials and don't add quota.
• Subscribe once to activate your account; every key works immediately.
• Create keys, revoke them, watch usage, and cancel anytime at /developers/keys.
• To rotate: create a new key, switch your app to it, then revoke the old one.

Endpoint

GET /api/v1/rent-estimate

Parameters

address	string — full street address (geocoded). Provide this, or zip, or lat+lon.
zip	string — 5-digit ZIP code.
lat, lon	number — coordinates.
bedrooms	integer — 0–4+. Default 2.

Example

Request

curl "https://fia.rent/api/v1/rent-estimate\
  ?address=1524+S+6th+St+Milwaukee+WI&bedrooms=2" \
  -H "x-api-key: fia_live_..."

Response

{
  "query": { "zip": "53204", "bedrooms": 2, "lat": 43.01, "lon": -87.92 },
  "estimate": 985,
  "currency": "USD",
  "low": 887,
  "high": 1084,
  "method": "ai_grounded",
  "tier": "pro",
  "sources": { "census_baseline": 950, "comparables": 4 },
  "insight": "Con base en la mediana del Censo ($950) y 4 comparables
    en Fía, ~$985/mes es razonable para 2 recámaras. Es una estimación.",
  "provider": "Fía · Wellness Labs LLC",
  "disclaimer": "Estimación informativa. No es un avalúo."
}

Response fields

estimate	Estimated fair monthly rent (USD), or null if there isn't enough data.
low / high	Confidence range around the estimate.
method	How it was derived (see below).
sources	census_baseline value + count of Fía comparables used.
insight	AI market rationale — Pro & Business plans only.
tier	Your plan (free / pro / business).

Property endpoint

What public records say about one address: a HUD rent benchmark anywhere in the US, plus the assessed value and an estimated property tax where we hold parcel data. Same key, same quota.

GET /api/v1/property

Parameters

address	string — full street address (geocoded). Or pass zip + street + house yourself.
zip	string — 5-digit ZIP. Required if you don't pass address.
street, house	string / integer — needed to match a parcel and return an assessment.
bedrooms	integer — 0–4. Default 2. Selects which HUD rent is returned.

Request

curl "https://fia.rent/api/v1/property\
  ?address=1524+S+6th+St+Milwaukee+WI&bedrooms=2" \
  -H "x-api-key: fia_live_..."

Response

{
  "query": { "zip": "53204", "house": 1524, "street": "South 6th Street", "bedrooms": 2 },
  "market": { "slug": "milwaukee-wi", "name": "Milwaukee", "state": "WI" },
  "coverage": { "rent": true, "assessment": true, "assessmentAvailableHere": true },
  "rent": {
    "monthly": 1140, "bedrooms": 2, "source": "hud_safmr",
    "area": "Milwaukee-Waukesha, WI MSA", "fiscalYear": 2026,
    "note": "HUD Small Area Fair Market Rent — a voucher payment standard,
      not observed asking rent."
  },
  "assessment": {
    "assessedTotal": 198000, "taxkey": "4290123000", "units": 2, "yearBuilt": 1912,
    "source": "City of Milwaukee Master Property File (MPROP), CC BY"
  },
  "propertyTax": {
    "annualEstimate": 4118, "ratePer1000": 20.8, "rateYear": 2025,
    "method": "assessed value ÷ 1,000 × net tax rate"
  },
  "tier": "pro",
  "provider": "Fía · Wellness Labs LLC"
}

Coverage is explicit. marketis null outside the areas where we hold local records — that's the normal case, not an error, and coverage.assessmentAvailableHeredistinguishes "we don't cover this area" from "we do, but no parcel matched that address". An assessed value is not an appraisal and an estimated tax is not a tax bill.

Method values

census_baseline	Census median gross rent for the area.
comps	Fía comparable listings in the area.
blended	Average of the Census baseline and comparables.
ai_grounded	AI-refined estimate reasoned over the real data (Pro+).
insufficient_data	No baseline or comparables — estimate is null.

Errors

400	Missing address, zip, or lat+lon.
401	Missing or invalid API key.
429	Rate limit (30/60s) or monthly quota exceeded.

Rate limits & plans

• 30 requests / 60s per key and per IP.
• Monthly quota — Standard 10,000 · Business custom, shared across all keys on your account. All plans are paid (no free tier).
• The AI insight is included on all paid plans.

Estimates are informational, not appraisals. Fía Rent API · a service of Wellness Labs LLC.