Pull a house price index into a spreadsheet with the REST API

This is the smallest useful thing you can do with the REST API: one endpoint, one area, a monthly series you can chart. It uses the repeat-sales house price index, so the number moves only when the same properties sell again, not when the mix of what sold changes. The call is free.

Step 1: create an API key

Sign in to the API & MCP Hub and create a key. It is shown once; copy it somewhere safe. A new account starts with free credits, and the endpoint in this guide does not use any. Keys are for code; if you are using an AI assistant, connect the MCP server instead and skip this guide.

Step 2: make the call

Replace the area code with any postcode district (SE22) or local authority name (Lewisham), and set area_type to district or lad to match.

curl "https://api.marketcode.ai/v1/market/index-series?area_code=SE22&area_type=district&limit=36" -H "Authorization: Bearer $MARKETCODE_API_KEY"

The response is JSON with three parts:

• data.area: the area as the warehouse knows it, with its id, which the per-area endpoints such as energy profile and agent activity key on.
• data.series: one row per month, newest last, each with the period, the index level, the twelve-month change where there is one, and a flag for whether the point is settled or forecast.
• data.provenance: the method, the base period, the publication frequency and the last settled period. Read this before you chart anything.

Every response also carries credits_charged and credits_remaining. For this call the first is zero.

Step 3: load it

Excel. Data → Get Data → From Other Sources → From Web. Choose Advanced, paste the URL, and add an HTTP header Authorization with the value Bearer followed by your key. In Power Query, expand data → series → To Table, then expand the record columns. Set the period column to text: a value like 2025-12 is a month, not a date, and Excel will otherwise guess.

Google Sheets. Sheets cannot send headers from a plain formula, so use Apps Script: UrlFetchApp.fetch(url, {headers: {Authorization: 'Bearer ' + key}}), parse the JSON, and write series to a range. Keep the key in Script Properties, not in a cell.

Anything else. Python's requests, or a scheduled job, with the same header. The REST API page has the OpenAPI document.

Step 4: chart it honestly

Three things the response tells you that a chart should show:

• Forecast points are marked. The last few months carry a forecast flag because HM Land Registry registrations arrive for weeks after completion. Plot them dashed, or stop the line at the last settled period in provenance.
• The base period is stated. An index of 130 means 30% above the base month, not a price. If you want pounds, multiply by a reference price from market_facts for the base period.
• The method may be national. For a thin district the series can be the national index standing in for a local one, and provenance says so. A chart that labels that as SE22 is wrong.

What to add next

The asking-price and asking-rent indices sit at /v1/market/asking-index and /v1/market/rent-index with the same parameters, and lead the sold index by months. Registered sales per month for a district are at /v1/market/volume-series. All free. Put the three on one chart and you have the district's last five years in one picture.