OpenCMA Public API

A free, key-free REST API for Ohio and California property data, nightlife scores, and map deep-links. No authentication required.

Base URL: /api/v1 · All endpoints return JSON · CORS open (*)

1. Overview

The OpenCMA public API exposes two endpoints under /api/v1. No API key, no account, no token. Every response is served with an open CORS header (Access-Control-Allow-Origin: *), so you can call it directly from a browser, a server, or an AI agent.

Base URL/api/v1AuthNoneCORSOpen (*)Rate limit60 requests / minute / IPEdge cacheSuccessful GETs cached 24 hoursFormatJSON (all responses)

Responses include rate-limit headers on every request. On a 429 you will also receive a Retry-After header. See § Rate limits for full details.

2. GET /api/v1/nightlife

Covered cities only

Returns a nightlife score for a geographic point from precomputed grid data. Coverage is limited to four metro areas; queries outside coverage return a 404.

Query Parameters

Parameter	Type	Required	Description
`lat`	number	One of lat/lng or address	Latitude (WGS 84, decimal degrees)
`lng`	number	One of lat/lng or address	Longitude (WGS 84, decimal degrees)
`address`	string	One of lat/lng or address	Street address; geocoded server-side when lat/lng omitted
`band`	18 \| 20 \| 25 \| 30	No (default 20)	Peer age cohort for the nightlife score. Selects the age-demographic component used in the composite formula.

Response

{
  "query": { "lat": 41.4993, "lng": -81.6919, "band": 20 },
  "city": { "slug": "cleveland", "name": "Greater Cleveland, OH" },
  "cell": { "lat": 41.4992, "lng": -81.6918, "distanceMiles": 0.01 },
  "components": { "go": 0.91, "stay": 0.88, "p18": 0.9, "p20": 1, "p25": 0.98, "p30": 0.87 },
  "composite": 80,
  "tier": "Vibrant",
  "nearestCluster": {
    "name": "Downtown Cleveland",
    "lat": 41.4993,
    "lng": -81.6919,
    "distanceMiles": 0
  }
}

Field Notes

Field	Notes
`components`	Each value is 0–1. `go` = venue density score; `stay` = open-late score; `p18/p20/p25/p30` = age-band demographic weight.
`composite`	0–100. Formula: `round(go × stay × p<band> × 100)`
`tier`	One of: Vibrant (≥ 80), Strong (≥ 65), Solid (≥ 50), Some options (≥ 35), Quiet (≥ 20), Sleepy (< 20)
`nearestCluster`	Named nightlife district nearest to the queried point. `null` if no named cluster detected.
`cell`	Center of the precomputed grid cell that contains the queried point. `distanceMiles` is the snap distance from query point to cell center.

Covered Cities

Slug	Name
`cleveland`	Greater Cleveland, OH
`columbus`	Greater Columbus, OH
`bay-area`	SF Bay Area (SJ to SF + East Bay), CA
`seattle`	Greater Seattle, WA

Error Responses

Status	Body (JSON)	Cause
400	`{"error":"lat & lng or address required"}`	Neither lat/lng nor address provided
404	`{"error":"Address not found"}`	Geocoder returned no results for the given address
404	See below	Point is outside all covered cities

{
  "error": "No nightlife coverage for this location",
  "supportedRegions": [
    "SF Bay Area (SJ to SF + East Bay), CA",
    "Greater Columbus, OH",
    "Greater Cleveland, OH",
    "Greater Seattle, WA"
  ],
  "hint": "Pass lat/lng or an address inside a covered city: cleveland, columbus, bay-area, seattle."
}

3. GET /api/v1/property

OH & CA only

Returns a curated property summary for a US street address. Aggregates county assessor data, FEMA flood zones, Census demographics, and more into a single response. Supported states: Ohio and California.

Query Parameters

Parameter	Type	Required	Description
`address`	string	Yes	Full US street address, e.g. `1619 Mistletoe Dr, Cleveland, OH`

Response

{
  "address": "1619 Mistletoe Dr, Cleveland, OH",
  "countyTier": "full",
  "location": {
    "lat": 41.5,
    "lng": -81.7,
    "countyFips": "035",
    "tractCode": "107101"
  },
  "parcel": {
    "parcelId": "123",
    "owner": "JANE DOE",
    "yearBuilt": 1920,
    "buildingSqft": 1450,
    "lotAcres": 0.1,
    "beds": 3,
    "baths": 1,
    "useCode": "R-1",
    "useDescription": "single_family"
  },
  "value": {
    "assessedTotal": 120000,
    "assessedLand": 20000,
    "assessedBuilding": 100000,
    "marketTotal": 342000
  },
  "taxRate": {
    "municipal": 0.02,
    "schoolDistrict": 0.0125,
    "schoolDistrictName": "Cleveland Municipal SD"
  },
  "scores": {
    "location": 80,
    "environment": 65,
    "valueTrend": 70,
    "taxBurden": 66,
    "investment": 71
  },
  "flood": {
    "zone": "X",
    "riskLevel": "minimal",
    "isSpecialFloodHazardArea": false
  },
  "demographics": {
    "medianHouseholdIncome": 55000,
    "population": 4000,
    "medianAge": 38,
    "ownerOccupiedPct": 62
  },
  "nightlife": {
    "composite": 80,
    "tier": "Vibrant",
    "components": {
      "go": 0.91,
      "stay": 0.88,
      "p18": 0.9,
      "p20": 1,
      "p25": 0.98,
      "p30": 0.87
    },
    "nearestCluster": {
      "name": "Downtown Cleveland",
      "distanceMiles": 0.3
    }
  }
}

Field Notes

Field	Notes
`countyTier`	`"full"` = dedicated county scraper; `"basic"` = limited/fallback data (Ohio OGRIP statewide parcels, or any California county). Many parcel fields may be `null`. For California, actual data richness varies by county regardless of this flag.
`value`	All amounts in USD. In Ohio, assessed value ≈ 35% of market value (state law). In California, assessed value reflects Prop 13 purchase-price base (often well below market).
`taxRate`	Decimal fractions: `0.02` = 2%. `municipal` and `schoolDistrict` are Ohio income tax rates; `null` when no tax applies or data unavailable.
`scores`	0–100, higher is better. Aggregated from public-source data; not a substitute for a licensed appraisal.
`flood.riskLevel`	One of: `minimal`, `moderate`, `high`, `very_high`. Derived from FEMA zone code.
`demographics`	US Census ACS tract-level data. `null` if Census lookup fails.
`nightlife`	Present only for addresses in a covered city (Cleveland, Columbus, Bay Area, Seattle). Omitted otherwise. The embedded score is computed at `band=20` (20–34 cohort); the full `components` object is included so callers can recompute other bands. Use `/api/v1/nightlife?...&band=` for a specific cohort.
Numeric fields	`null` when unknown — do not assume 0.

Error Responses

Status	Body (JSON)	Cause
400	`{"error":"address required"}`	No address parameter provided
404	`{"error":"Address not found"}`	Geocoder returned no results for the given address
404	See below	Address is in a state without property data

{
  "error": "Property data not available for this state",
  "supportedRegions": ["OH", "CA"],
  "hint": "Use a street address within Ohio or California."
}

4. Rate Limits

The API enforces a limit of 60 requests per minute per IP address. Every response includes the following headers:

Header	Value
`X-RateLimit-Limit`	Total requests allowed per window (60)
`X-RateLimit-Remaining`	Requests remaining in the current window
`X-RateLimit-Reset`	Seconds until the window resets
`Retry-After`	Seconds to wait before retrying (only on 429)

Successful GETs are edge-cached for 24 hours, so cached responses do not count against your rate limit. If you hit the limit you will receive an HTTP 429 Too Many Requests with a JSON body: {"error":"Rate limit exceeded"}.

5. Examples

Nightlife — curl

curl "https://<site>/api/v1/nightlife?lat=41.4993&lng=-81.6919"

Property — curl

curl "https://<site>/api/v1/property?address=1619+Mistletoe+Dr,+Cleveland,+OH"

JavaScript fetch()

// Nightlife score
const nightlife = await fetch(
  'https://<site>/api/v1/nightlife?lat=41.4993&lng=-81.6919&band=25'
).then(r => r.json());

console.log(nightlife.composite, nightlife.tier);
// → 80 "Vibrant"

// Property report
const property = await fetch(
  'https://<site>/api/v1/property?address=' +
  encodeURIComponent('1619 Mistletoe Dr, Cleveland, OH')
).then(r => r.json());

console.log(property.parcel.yearBuilt, property.flood.riskLevel);
// → 1920 "minimal"

6. Map Share Links

The /map page accepts query parameters that set the initial viewport, city layer, and pins. Share URLs can be constructed programmatically.

URL Format

/map?pins=lat,lng[,label];...&center=lng,lat,zoom&city=<slug>

Parameter	Format	Description
`pins`	`lat,lng[,label];...`	Semicolon-delimited list of pins. Each pin is `lat,lng` or `lat,lng,label` where `label` is `encodeURIComponent`-encoded.
`center`	`lng,lat,zoom`	Initial map center (longitude first, MapLibre convention) and zoom level.
`city`	string slug	Activates the precomputed nightlife layer for the given city. Slugs: `cleveland`, `columbus`, `bay-area`, `seattle`.

Example — Build a share URL in JavaScript

const pins = [
  { lat: 41.4993, lng: -81.6919, label: 'Tremont $450k' },
  { lat: 41.50, lng: -81.70, label: 'HQ' },
];
const param = pins
  .map(p => `${p.lat.toFixed(4)},${p.lng.toFixed(4)},${encodeURIComponent(p.label)}`)
  .join(';');
const url = `https://<site>/map?city=cleveland&pins=${param}`;

Produces: /map?city=cleveland&pins=41.4993,-81.6919,Tremont%20%24450k;41.5000,-81.7000,HQ

Pin state also persists in localStorage for 24 hours and propagates across tabs. Coords-only pins (no label) are also valid.

7. For LLMs & Agents

OpenCMA follows the llms.txt convention for machine-readable API summaries. AI agents and LLM pipelines can fetch a compact, structured description of all endpoints, field semantics, and share-link formats without parsing this HTML page.

Fetch /llms.txt — a machine-readable summary you can fetch and parse — and include it in your system prompt or tool context. It covers both endpoints, all field types and null semantics, the composite formula, tier names, coverage, and share-link format.

# In your agent / system prompt:
const apiDocs = await fetch('https://<site>/llms.txt').then(r => r.text());
// → inject apiDocs into context before calling /api/v1/*

Note: OpenCMA data is aggregated from public sources (county assessors, FEMA, US Census, OpenStreetMap). It is informational only and is not a substitute for a licensed appraisal, title search, or professional inspection.