How to Integrate Lovable with CoStar

CoStar API access is not self-service. To get API credentials, visit api.costar.com and contact CoStar's developer relations team, or work with your CoStar account manager if you already have a subscription. API access is granted based on your subscription tier and use case — the available endpoints depend on whether your subscription includes property data, comparables, market analytics, or all three. CoStar provides API documentation at developer.costar.com once access is granted. The documentation covers the available endpoints, rate limits (typically 100-500 requests per minute depending on subscription), response formats, and field definitions. Review the documentation for your subscription level before building your Lovable integration. Once approved, CoStar provides an API key (sometimes in the form of an API key plus a username/password depending on the endpoint). Note the base URL for your environment — CoStar may provide sandbox and production endpoints. Store the sandbox key during development and switch to production credentials before launch. If you are building a Lovable prototype to demonstrate to your CoStar account team or to evaluate the integration before committing to API access, you can mock the CoStar data structure in your Edge Function to build the UI while waiting for API approval.

In Lovable, click the '+' button next to the Preview panel to open the Cloud tab, then navigate to Secrets. Add the following secrets: - COSTAR_API_KEY: your CoStar API key - COSTAR_API_BASE_URL: the base URL for CoStar's API (e.g., https://api.costar.com or a versioned URL like https://api.costar.com/v1) If CoStar requires both an API key and a username/password (which some endpoint tiers do), also add COSTAR_USERNAME and COSTAR_PASSWORD as separate secrets. The Edge Function can construct the appropriate authentication header — either a simple API key header or a Basic Auth header combining username and password. CoStar's API is commercial and expensive — protecting these credentials is important not just for security but for billing. An exposed API key used by unauthorized parties could incur significant overage charges. Lovable's security system blocks approximately 1,200 hardcoded API keys daily, but never paste the CoStar key in the chat panel or in any frontend code.

Create the Edge Function that proxies CoStar API requests. The function accepts the endpoint path and query parameters from the frontend, constructs the full CoStar API URL, adds the authentication headers, and returns the response. CoStar's API authentication typically uses an API key in a request header (commonly X-API-Key or Authorization: Bearer). Check your CoStar API documentation for the exact header format — this varies by subscription tier and endpoint family. Some CoStar endpoints use Basic Auth with username and password. The Edge Function should handle CoStar's specific error responses: 401 for invalid API key, 403 for endpoints not covered by your subscription, 429 for rate limit exceeded (implement exponential backoff), and 404 for properties that don't exist in CoStar's database. Returning descriptive error messages to the frontend improves the user experience when CoStar data is unavailable. Rate limiting is important for CoStar — their API has strict limits, and hitting them repeatedly can result in temporary access suspension. Implement request queuing or retry logic in the Edge Function for high-traffic scenarios.

1// supabase/functions/costar-proxy/index.ts
2import { serve } from "https://deno.land/std@0.168.0/http/server.ts";
3
4const corsHeaders = {
5  "Access-Control-Allow-Origin": "*",
6  "Access-Control-Allow-Headers": "authorization, x-client-info, apikey, content-type",
7  "Access-Control-Allow-Methods": "POST, OPTIONS",
8};
9
10serve(async (req: Request) => {
11  if (req.method === "OPTIONS") {
12    return new Response("ok", { headers: corsHeaders });
13  }
14
15  try {
16    const apiKey = Deno.env.get("COSTAR_API_KEY");
17    const baseUrl = Deno.env.get("COSTAR_API_BASE_URL");
18
19    const { endpoint, method = "GET", params, body } = await req.json();
20
21    let url = `${baseUrl}${endpoint}`;
22    if (params && method === "GET") {
23      url += "?" + new URLSearchParams(Object.entries(params).map(([k, v]) => [k, String(v)])).toString();
24    }
25
26    const response = await fetch(url, {
27      method,
28      headers: {
29        "Authorization": `Bearer ${apiKey}`,
30        "Content-Type": "application/json",
31        "Accept": "application/json",
32      },
33      ...(body && method !== "GET" ? { body: JSON.stringify(body) } : {}),
34    });
35
36    if (response.status === 429) {
37      return new Response(JSON.stringify({ error: "CoStar rate limit exceeded", retryAfter: response.headers.get("Retry-After") || "60" }), {
38        status: 429, headers: { ...corsHeaders, "Content-Type": "application/json" },
39      });
40    }
41
42    if (response.status === 403) {
43      return new Response(JSON.stringify({ error: "This CoStar endpoint is not covered by your subscription" }), {
44        status: 403, headers: { ...corsHeaders, "Content-Type": "application/json" },
45      });
46    }
47
48    const data = await response.json();
49    return new Response(JSON.stringify(data), { status: response.status, headers: { ...corsHeaders, "Content-Type": "application/json" } });
50  } catch (error) {
51    return new Response(JSON.stringify({ error: error.message }), { status: 500, headers: { ...corsHeaders, "Content-Type": "application/json" } });
52  }
53});

With the Edge Function deployed, open Lovable chat and describe the property search UI. Provide the CoStar field names and endpoint structure from your API documentation so Lovable generates correct query parameters and response parsing. CoStar property search typically accepts parameters like: marketName or marketId, propertyType (office, industrial, retail, multifamily, mixed-use), minSize and maxSize in square feet, minVacancy and maxVacancy as percentages, propertyStatus (active, available, all), and pagination parameters like page and pageSize. CoStar property records include a rich set of fields: propertyId (CoStar's unique identifier), propertyName, address (street, city, state, zip), propertyType, buildingSize, yearBuilt, occupancyRate, numberOfFloors, parkingRatio, and owner/tenant information depending on your subscription level. For each property card in the results, link to CoStar's website using the propertyId in the URL format (costar.com/Properties/{propertyId}) so users can click through for more detail. This is a common pattern in CRE apps that surface CoStar data.

The most valuable CoStar data for CRE professionals is comparables and market analytics — the data that brokers use to price deals and investors use to validate underwriting assumptions. Once the basic property search works, extend the integration to show comps and market trends. Comparables (comps) are recent sale or lease transactions for similar properties in the same market. The CoStar comps API typically accepts a property ID or market/submarket/property type combination and returns transactions with: transaction date, price, price per square foot, cap rate (for sales), rent per square foot (for leases), tenant name (for leases), and seller/buyer information. Market analytics endpoints return time series data for a market and property type: vacancy rate over time, average asking rent over time, net absorption by quarter, new supply and demolitions, and future under-construction space. These power the charts that CRE investors expect in investment memos. For complex CoStar API integrations with custom data pipelines, scheduled pulls, or integration with proprietary deal databases, RapidDev's team can help design the full architecture.