OpenCompanies MCP server

OpenCompanies is also available as a Model Context Protocol (MCP) server. AI assistants such as Claude, ChatGPT, Cursor and VS Code can use it to search UK companies, look up officers and people with significant control, trace ownership, find connections and read accounts figures. It only reads the data (but for sending feedback, when you agree), needs no key, account or sign-in, and serves the same data, under the same licence, as the rest of this site.

Server URL

https://opencompanies.uk/mcp

Transport

Streamable HTTP

Authentication

None

Version

1.0.0

Connect

Every client needs only the server URL. When a client asks how to authenticate, choose no authentication.

Claude (claude.ai, Desktop and mobile)

Add OpenCompanies to Claude opens the Add custom connector dialog with the name and URL filled in; check them and click Add.

To add it by hand, go to Customize, then Connectors, and click Add custom connector. Enter the name OpenCompanies and the URL https://opencompanies.uk/mcp, and if the dialog asks about authentication, choose No sign-in. The connector then works in the Claude apps on desktop and mobile too. On Team and Enterprise plans an Owner adds it for everyone under Organization settings, Connectors, Add, Custom, Web (or with the prefilled admin link).

Claude Code

claude mcp add --transport http opencompanies https://opencompanies.uk/mcp

Add --scope project to share it through the project's .mcp.json, which looks like this:

{
  "mcpServers": {
    "opencompanies": {
      "type": "http",
      "url": "https://opencompanies.uk/mcp"
    }
  }
}

Prompts appear as slash commands such as /mcp__opencompanies__who_owns, and resources can be attached with @opencompanies:.

ChatGPT

Turn on developer mode under Settings, Security and login, Developer mode. Then go to chatgpt.com/plugins, select the plus button, give it a name and description, enter https://opencompanies.uk/mcp as the connection URL with no authentication, and create it. The search and fetch tools follow OpenAI's contract, so deep research can use them and cite opencompanies.uk pages.

Cursor

Add to Cursor, or put this in ~/.cursor/mcp.json (or .cursor/mcp.json in a project):

{
  "mcpServers": {
    "opencompanies": {
      "url": "https://opencompanies.uk/mcp"
    }
  }
}

VS Code

Install in VS Code, or add it to .vscode/mcp.json (the top-level key is servers):

{
  "servers": {
    "opencompanies": {
      "type": "http",
      "url": "https://opencompanies.uk/mcp"
    }
  }
}

From a terminal:

code --add-mcp '{"name":"opencompanies","type":"http","url":"https://opencompanies.uk/mcp"}'

OpenAI Codex

codex mcp add opencompanies --url https://opencompanies.uk/mcp

or in ~/.codex/config.toml:

[mcp_servers.opencompanies]
url = "https://opencompanies.uk/mcp"

Codex uses tools only, not prompts or resources.

Gemini CLI

gemini mcp add --transport http opencompanies https://opencompanies.uk/mcp

or in ~/.gemini/settings.json, where httpUrl (not url) selects Streamable HTTP:

{
  "mcpServers": {
    "opencompanies": {
      "httpUrl": "https://opencompanies.uk/mcp"
    }
  }
}

Windsurf (Devin Desktop)

Add it to mcp_config.json, which is at ~/.config/devin/mcp_config.json on macOS and Linux and %APPDATA%\devin\mcp_config.json on Windows:

{
  "mcpServers": {
    "opencompanies": {
      "serverUrl": "https://opencompanies.uk/mcp"
    }
  }
}

Zed

Use Settings, AI, MCP Servers, Add Server, Add Remote Server, or add it to your settings file:

{
  "context_servers": {
    "opencompanies": {
      "url": "https://opencompanies.uk/mcp"
    }
  }
}

Zed uses tools and prompts.

Goose

Run goose configure and add a remote extension (Streamable HTTP), or add it to ~/.config/goose/config.yaml:

extensions:
  opencompanies:
    name: OpenCompanies
    type: streamable_http
    uri: https://opencompanies.uk/mcp
    enabled: true
    timeout: 300

For one session only:

goose session --with-streamable-http-extension "https://opencompanies.uk/mcp"

MCP Inspector

To explore the server by hand, start the Inspector, choose Streamable HTTP and paste the URL:

npx @modelcontextprotocol/inspector

or use its command line (add --protocol-era modern to try the 2026-07-28 protocol):

npx @modelcontextprotocol/inspector --cli --transport http --server-url https://opencompanies.uk/mcp --method tools/list

Clients that only run local servers

A client that can only start local (stdio) servers can reach OpenCompanies through mcp-remote:

{
  "mcpServers": {
    "opencompanies": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://opencompanies.uk/mcp",
        "--transport",
        "http-only"
      ]
    }
  }
}

Things to ask

• Who ultimately owns Tesco PLC?
• What other companies have the directors of 00445790 run, and which have been dissolved?
• Which software companies (SIC 62012) were incorporated in the last 30 days in the M1 postcode district?
• Compare the last two years of accounts figures for Tesco PLC and J Sainsbury plc.
• What is registered at the postcode EC1V 2NX, and is it a registration hub?
• How are Tesco PLC and Tesco Stores Limited connected?

Tools

24 tools, all read-only except send_feedback, which sends a note to the people who run OpenCompanies (see feedback). Each returns structured data, repeated as JSON text, with opencompanies.uk links to cite. Tools marked heavy share a small number of slots (see limits).

Prompts

Prompts are ready-made research tasks that your client may offer as commands. Each one asks the assistant to use the tools above, cite its sources and list what it could not check.

Resources

Resources are documents a client can attach to a conversation. Their addresses are the same https URLs a browser opens, and reading one returns what the site serves, except that links in Markdown are made absolute.

Reference documents

Records by identifier

Try it with curl

The server is stateless, so every request stands on its own. A modern (2026-07-28) request carries its protocol version and client capabilities in params._meta and repeats the version, method and tool name in headers. A legacy client starts with initialize; later requests name the agreed version in the MCP-Protocol-Version header and need no session id, because none is ever issued.

Modern (2026-07-28): ask the server what it supports

curl -s https://opencompanies.uk/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -H 'MCP-Protocol-Version: 2026-07-28' \
  -H 'Mcp-Method: server/discover' \
  -d '{"jsonrpc":"2.0","id":1,"method":"server/discover","params":{"_meta":{"io.modelcontextprotocol/protocolVersion":"2026-07-28","io.modelcontextprotocol/clientCapabilities":{},"io.modelcontextprotocol/clientInfo":{"name":"curl","version":"1.0.0"}}}}'

Modern (2026-07-28): call get_company for 00445790

curl -s https://opencompanies.uk/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -H 'MCP-Protocol-Version: 2026-07-28' \
  -H 'Mcp-Method: tools/call' \
  -H 'Mcp-Name: get_company' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"get_company","arguments":{"company_number":"00445790"},"_meta":{"io.modelcontextprotocol/protocolVersion":"2026-07-28","io.modelcontextprotocol/clientCapabilities":{},"io.modelcontextprotocol/clientInfo":{"name":"curl","version":"1.0.0"}}}}'

Legacy (2025-11-25): the initialize handshake

curl -s https://opencompanies.uk/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-11-25","capabilities":{},"clientInfo":{"name":"curl","version":"1.0.0"}}}'

Legacy (2025-11-25): list the tools (no session to carry over)

curl -s https://opencompanies.uk/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -H 'MCP-Protocol-Version: 2025-11-25' \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/list"}'

Each of these answers is a single JSON response.

Limits and fair use

• Lists come a page at a time. Pass the next_cursor from one page as cursor to get the next. Searches and lists that cross many records stop after 1,000 rows, one company's officers or owners after 5,000, and one person's roles after 2,000; narrow the query to go further.
• Totals stop counting at 1,000 unless a nightly count exists, and total_is_capped says so.
• Each database query may run for 8 seconds, and each tool call for 20 seconds in all. A query that runs out of time returns a message suggesting how to narrow it.
• Tools marked heavy in the tools table run at most 2 at a time across the whole site. When they are all busy you get a short "busy" message; try again a few seconds later.
• A tool result is at most 60,000 characters, a resource at most 1 MiB, and a request body at most 64 KiB. A legacy batch holds at most 10 messages.
• Please keep automated use gentle, a few requests a second at most. Heavy traffic may be rate limited.
• Please cache what you fetch. For work across the whole register, use the bulk data rather than paging through the MCP server.

Data caveats

Only identifiers issued by Companies House establish that two records are the same person or company. Where Companies House issues none, as for people with significant control, filings are grouped into records instead, as described below.

• Officers. An officer record is keyed on an identifier Companies House issues to officers, so its officer appointments are confirmed as belonging to one officer record.
• People with significant control. A control record groups control filings that share the same name and birth month and year. Companies House issues no identifier for people with significant control, so the grouping is a strong lead rather than proof: two people with a common name and the same birth month and year would share one record.
• Possibly the same person: same name and birth month and year. Unconfirmed; people with common names often share these. Results label each possible match with how it was found and whether anyone has reviewed it.
• Dissolution. A company is treated as dissolved only when Companies House has recorded it, through its status or a dissolution date. Missing from a register snapshot is not dissolution, and dissolution is not failure: many solvent companies are struck off voluntarily.
• Disqualifications. Disqualification records come from Companies House's live disqualification feed since OpenCompanies began collecting it, not the full register. Possible matches are unconfirmed: match_basis says whether a record shares the name and birth month and year (name_and_birth_date), the name and birth year (name_and_birth_year) or only words of the name (name_only). No match does not mean a person is not disqualified; check the official register.
• Control. The register of people with significant control only covers holdings of more than 25% of shares or votes, the right to appoint or remove a majority of the board, and significant influence or control, so most shareholders with 25% or less never appear.
• Accounts. Figures come only from accounts filed electronically since 2008. A blank figure means it was not reported, not that it was zero, and figures are as filed, not verified.
• Not held. Charges, insolvency notices, shareholdings of 25% or less, sanctions and credit data. Missing data is not proof of absence.

The data guide explains them in full, with how people and companies are identified, and status.json says how current each part is.

Feedback

send_feedback lets an assistant send the people who run OpenCompanies a short note about these tools: something no tool could answer, an answer that was wrong or confusing, or an error that did not say what would work. Its description tells the assistant to show you the note and send it only once you agree.

What is kept: the note, its kind, the tool it names, the client's name and version, the protocol and server versions, and the time. Never your IP address: only a keyed hash of it, to limit each address to 10 notes a day. A note holding an email address, an IP address or a web address with a query string is refused. Notes are read only by the people who run OpenCompanies, and deleted after 365 days.

Protocol

• One endpoint, https://opencompanies.uk/mcp, speaking Streamable HTTP over POST.
• Modern clients use protocol version 2026-07-28: no handshake, per-request _meta, server/discover, and the MCP-Protocol-Version, Mcp-Method and Mcp-Name headers.
• Legacy clients use initialize with 2025-11-25, 2025-06-18 or 2025-03-26. A legacy request without the MCP-Protocol-Version header is treated as 2025-03-26, the only revision that allows batches (up to 10 messages). Older revisions never see fields added after them.
• Stateless: no sessions, no Mcp-Session-Id, no cookies and no GET stream. A GET from an MCP client gets 405; a browser gets this page.
• Every answer is a single JSON response but one: a modern client's subscriptions/listen gets a short event stream that acknowledges it and ends at once, since nothing is ever pushed.
• Tools, resources, prompts and completions. No logging, resource subscriptions, change notifications, sampling, elicitation or tasks.
• No OAuth and no API keys: the server never asks a client to sign in. Requests from every origin are allowed (CORS).
• Discovery documents: the server card and the AI catalog. The site's source also holds a server.json for the official MCP Registry.

OpenCompanies is an open, read-only map of UK companies from Companies House data (Open Government Licence v3.0). Companies are identified by company_number, people by person_id. Identity: only Companies House identifiers establish that two records are the same. Records described as possibly the same person share a name and birth month and year but are unconfirmed; present them as possible matches, not facts. A company is dissolved only when Companies House records it. Missing data is not proof of absence.

It holds companies (live and dissolved), officers, people with significant control (PSC), company ownership, corporate groups, registered addresses, SIC codes and accounts figures.

Coverage: control data only covers holders of more than 25% of shares or votes, or with the right to appoint most directors or significant influence; smaller shareholders usually do not appear. Accounts figures exist only for electronic filings from 2008, and a blank figure means not reported, not zero. Disqualification records are partial. Charges, insolvency notices, shareholdings of 25% or less, sanctions and credit data are not held.

Scale: some addresses host thousands of companies (formation agents) and some people hold thousands of appointments (nominee directors), so lists are capped and paged; pass next_cursor back as cursor for more.

Start with search_companies or search_people to get a company_number or person_id. Describe a company's state with status_group; is_active only means it is still on the register. The guide (https://opencompanies.uk/mcp/guide.md) explains these, identity_basis and the limits.

Cite the opencompanies.uk links in results. The official Companies House register is authoritative where they differ. Attribution: Contains public sector information licensed under the Open Government Licence v3.0. Source: Companies House.

If no tool can answer what the user asked, or an answer looks wrong, offer to tell OpenCompanies with send_feedback, and send it only once the user agrees.

Licence and attribution

The data comes from Companies House and is reused under the Open Government Licence v3.0. When you publish something built from it, include this attribution: Contains public sector information licensed under the Open Government Licence v3.0. Source: Companies House. Tool results carry the same attribution in every answer.

OpenCompanies is an independent project and is not affiliated with Companies House. The official register is the authoritative source: where anything here differs from it, Companies House's own entry takes precedence.

OpenCommons

OpenCompanies is one of the OpenCommons sites. Their MCP servers keep one contract (identity, paging, results, errors and feedback), so an assistant connected to more than one finds the same conventions in each. Where a record has a counterpart on another of the sites, its result links to it under external_links.

• OpenCharities, UK charities from the three regulators' registers: England and Wales, Scotland and Northern Ireland: https://opencharities.uk/mcp
• OpenPostcodes, every live UK postcode from the ONS Postcode Directory, with its location, geographies and nearest services: https://openpostcodes.uk/mcp
• OpenProperties, residential property sales in England and Wales from HM Land Registry's Price Paid Data: https://openproperties.uk/mcp