OnTheMarket
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.
More than an index entry, but the surface is still mostly links rather than artifacts — the cohort most likely to move a full band from modest, well-targeted work.
API Evangelist profiles OnTheMarket the way a machine reads it — 2 machine-readable artifacts across 1 API, pulled from the provider's own public surface and indexed so a developer, an analyst, or an AI agent can evaluate it against every other provider on the network.
Every provider in the network is reduced to the same set of machine-readable artifacts — OpenAPI contracts, event specifications, GraphQL schemas, runnable collections, pricing and rate-limit signals, security posture, OAuth scopes, and the agent surfaces (MCP servers and skills) that let software drive the API on its own. We profile them because the interface is the part of a company you can actually inspect: it is a truer signal of what a provider does than any marketing page. From those artifacts we compute the Kin Score — OnTheMarket scores 18.1/100 (emerging), with a separate agent-readiness read of 0/100 (human only). The full breakdown is below, followed by every artifact we hold — each card links through to its machine-readable definition on apis.io.
Kin Score
This is the API Evangelist rating — a single, repeatable read computed from the artifacts on this page. Green fill is points earned; the red track is points possible, so every bar shows earned-versus-possible at a glance.
Kin Score
How this is scored →scored 2026-07-27 · rubric v0.5
How we profile OnTheMarket
Each block below is one kind of artifact we hold for OnTheMarket. For each we say what it is and why it earns a place in the profile, then list every one we've indexed — capped at two rows, scroll within the panel for the rest.
APIs 1
Each API is captured as its own OpenAPI definition — every operation, parameter, and response. This is the single most useful machine-readable description of what an API does, and it's what lets us score, lint, mock, and generate against it without asking the provider for anything.
Individual APIs this provider publishes, each with its own machine-readable definition.
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 Posture 1
Authentication, domain security, vulnerability disclosure, and trust-center signals — the evidence that a provider takes security seriously enough to document it. We profile it because you can't govern what you can't see.
Authentication, domain security, vulnerability disclosure, and trust-center signals.
Resources
Every other property we hold for OnTheMarket — documentation, portals, status pages, policies, and corporate surface — grouped by the job it does, following the integrator's arc from getting started to running in production.
Get Started 2
Portal, sign-up, and the first successful call
Agent Surfaces 2
MCP servers, agent skills, and machine-readable catalogs
Design & Contract 2
Pagination, idempotency, versioning, errors, and events
Build 2
SDKs, sample code, and the tooling you integrate with
Access & Security 1
Authentication, authorization, and security posture
Operate 2
Status, limits, changes, and where to get help
Commercial 2
Pricing, plans, and the legal terms of use
Company 6
The organization behind the API
Other 1
Properties that don't map to a standard resource type
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