# OnTheMarket

**Canonical:** https://apis.io/providers/onthemarket/  
**Website:** https://www.onthemarket.com/  
**APIs profiled:** 1

OnTheMarket is the third-largest residential property portal in the United Kingdom, operating onthemarket.com. It was founded in 2013 by Agents' Mutual Limited as an agent-owned challenger to Rightmove and Zoopla, listed on AIM as OnTheMarket plc, and was acquired outright by CoStar Group in December 2023 for approximately GBP 99 million. In a market with no MLS and no cooperative listing standard, OnTheMarket sits at the demand end of the value chain: consumers search the portal, and listings arrive from member estate agents' CRM systems rather than from a shared data pool. Its API posture is honest and narrow. There is no public developer portal — developer., developers., api. and docs.onthemarket.com do not resolve, and /developers, /api, /docs, /openapi.json, /swagger.json and /api-docs all return 404 on the main site. What does exist is a member-only integration surface: the OnTheMarket Real Time Datafeed (RTDF), a Rightmove-RTDF-compatible feed API served from the live, OnTheMarket-operated host realtime-api.onthemarket.com, used by agency CRM vendors to push listings and pull branch enquiries on behalf of member agents. No machine-readable contract for it is published anywhere; OnTheMarket's developer guide is distributed under agreement, and every path on the host returns 404 to an anonymous caller. There is no RESO Web API or Data Dictionary certification, no OData $metadata document and no Universal Property Identifier anywhere in the stack — RESO is a North American construct and the UK has never adopted it, so "certified but unreachable" does not apply here; there is no certification layer in this market at all. OnTheMarket publishes no open data. The genuinely open UK property layer belongs to the public sector — HM Land Registry Price Paid Data and Ordnance Survey — and none of it comes from the portals. OnTheMarket's own Terms of Use go further than most and expressly forbid automated access to any page other than the home page.

## Kin Score — 16.2 / 100 (emerging)

Scored 2026-08-20 under rubric 0.12.0. Trend: flat (+0.0 from 16.2).

| Facet | Score |
|---|---|
| Discoverability | 75.9 |
| Contract Quality | 0.0 |
| Governance | 0.0 |
| Contract Governance | 0.0 |
| Operational Transparency | 2.6 |
| Developer Ergonomics | 7.1 |
| Commercial Clarity | 34.2 |
| Access Clarity | 34.2 |

## Agent readiness — 0.0 (human-only)

| Dimension | Value |
|---|---|
| Spec Presence | no |
| Agentic Access | no |
| Reversibility Documented | no |
| MCP Server | no |
| Auth Clarity | no |
| Idempotency | no |
| Error Semantics | no |
| OpenAPI Examples | no |
| Rate Limit Signal | no |
| Event Surface Described | no |
| Agent Skills | no |
| Well Known Catalog | no |
| Consent Identity | no |
| Agent Card | no |
| Dry Run Mode | no |

## Access

Paid · OnTheMarket agent membership and a data-feed agreement required — onboarding: unknown, pricing: paid, trial: no (confidence: high).

## APIs (1)

- **OnTheMarket Real Time Datafeed (RTDF) API** — OnTheMarket's member-only feed API for estate-agency CRM software. It is modelled on the Rightmove Real Time Datafeed (RTDF/ADF) specification, with OnTheMarket-specific differe...

## Security (1)

- **Onthemarket Domain Security** — TLSv1.3 · HSTS · DMARC

## Tags

Real-Estate, United Kingdom, Property Listings, Property Portal, PropTech, Rentals, Estate Agents, Data Feed, New Homes, Commercial Real Estate

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Profiled by [API Evangelist](https://apievangelist.com) and published on [APIs.io](https://apis.io/providers/onthemarket/). Scores are computed from the provider's own public artifacts under a published rubric.