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Connect to the Sign Customiser MCP server

Sign Customiser is the platform sign makers use to sell custom signs online. This server exposes one merchant's store: its customisers, the option families and pricing they sell at, and the products, orders and quotes around them. Everything below is fact, in the order a client needs it.

At a glance

  • Endpoint https://web.signcustomiser.com/mcp
  • Transport Streamable HTTP
  • Method POST, with Accept: application/json, text/event-stream
  • Protocol revisions 2025-11-25, 2025-06-18, 2025-03-26, 2024-11-05
  • Authorization OAuth 2.1, authorization code with PKCE S256
  • Dynamic client registration Available, RFC 7591, public clients only
  • Tools 39, or 44 with the mcp:advanced scope
  • Tenancy One token is bound to one store for its whole life

Discovery

An unauthenticated request to the endpoint answers with the pointer that starts discovery:

HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer resource_metadata="https://web.signcustomiser.com/.well-known/oauth-protected-resource/mcp"
  • https://web.signcustomiser.com/.well-known/oauth-protected-resource/mcp RFC 9728 protected-resource metadata. Also served at /.well-known/oauth-protected-resource with the same document.
  • https://web.signcustomiser.com/.well-known/oauth-authorization-server RFC 8414 authorization-server metadata. Also served at /.well-known/oauth-authorization-server/mcp.
  • https://web.signcustomiser.com/oauth/register RFC 7591 dynamic client registration. No secret is issued or accepted. Redirect URIs must be HTTPS or loopback HTTP, matched exactly.
  • https://web.signcustomiser.com/oauth/authorize Authorization endpoint. PKCE S256 is mandatory. Send resource=https://web.signcustomiser.com/mcp per RFC 8707.
  • https://web.signcustomiser.com/oauth/token Token endpoint. Grants: authorization_code, refresh_token. Access tokens last 60 minutes, refresh tokens 30 days and rotate on use.
  • https://web.signcustomiser.com/oauth/revoke RFC 7009 revocation. Authenticate with the client_id the token was issued to.

The authorization response carries no RFC 9207 iss parameter, so take issuer assurance from discovery. A token is bound to one store, and the binding survives refresh rotation. Nothing a client sends can change which store it acts for.

Scopes

Request the smallest set that covers the work. A tool whose scope the merchant declined answers with an insufficient_scope error naming what it needed, rather than failing quietly.

  • customisers:read Read customisers and every option family they own.
  • customisers:write Create and change customisers and their option records.
  • pricing:read Read a customiser's pricing document and pricing model.
  • pricing:write Replace or merge a customiser's pricing document.
  • products:read Read products created from a customiser.
  • products:write Record integration products against a customiser.
  • orders:read Read orders and their design, production and delivery details.
  • orders:write Create orders. An order can reach a manufacturer.
  • quotes:read Read quote and custom-design submissions.
  • webhooks:read Read webhook subscriptions and available event types.
  • webhooks:write Create, change and delete webhook subscriptions.
  • store:read Read the store record, its subscription and its granted scopes.
  • analytics:read Read the order and revenue summary.
  • mcp:advanced Reveal the five advanced catalogue tools. Grants no data on its own; each operation still needs the scope above that matches it.

Client configuration

Claude Code:

claude mcp add --transport http sign-customiser https://web.signcustomiser.com/mcp

Run /mcp afterwards and choose Authenticate to complete the browser consent step.

Cursor, and any other client that reads an mcp.json. In Cursor that is .cursor/mcp.json in the project, or ~/.cursor/mcp.json globally:

{
  "mcpServers": {
    "sign-customiser": {
      "type": "http",
      "url": "https://web.signcustomiser.com/mcp"
    }
  }
}

Clients that infer the transport from the URL ignore "type". Leave it in; it is harmless where it is not needed.

Codex, in ~/.codex/config.toml:

[mcp_servers.sign_customiser]
url = "https://web.signcustomiser.com/mcp"

Claude on the web and Claude Desktop: Settings > Connectors > Add custom connector, then paste the endpoint URL. ChatGPT: Settings > Connectors, add a custom connector with the endpoint URL. Developer mode is required while a connector is unlisted.

MCP Inspector: run npx @modelcontextprotocol/inspector, connect with transport Streamable HTTP, and leave protocolEra at legacy. This server answers the initialize family of revisions and does not answer the 2026-07-28 server/discover family, so a run configured with modern fails to negotiate by design.

First call

List the tools the connection can see:

curl -sS https://web.signcustomiser.com/mcp \
  -H "Authorization: Bearer $SIGN_CUSTOMISER_MCP_TOKEN" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Then identify the store. get_store takes no arguments, needs store:read, and reports which scopes the merchant approved, which is the cheapest way to find out what the rest of the session can do:

{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "tools/call",
  "params": {
    "name": "get_store",
    "arguments": {}
  }
}

The result:

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "Connected to the universal store \"Demo Signs\" (id 12)."
      }
    ],
    "structuredContent": {
      "request_id": "req_01jz9x2k7c8f3m5n6p7q8r9s0t",
      "store": { "id": 12, "name": "Demo Signs" },
      "id": 12,
      "name": "Demo Signs",
      "platform": "universal",
      "plan": "starter",
      "currency": "GBP",
      "integrations": [
        {
          "object": "integration",
          "id": 17,
          "type": "custom",
          "name": "Warehouse bridge",
          "enabled": true
        }
      ],
      "scopes": ["store:read", "customisers:read"],
      "created_at": "2026-01-12T03:14:15Z"
    },
    "isError": false
  }
}

Every tool returns structuredContent alongside the text summary, and every result carries the request_id and the store it acted on. List tools return an opaque cursor; pass it back unchanged rather than building one.

Write conventions

  • Reads and writes are separate tools. Nothing changes a store unless its name says so.
  • Every write that supports it takes dry_run: true and returns the same validation verdict without applying anything. Call it that way first.
  • Deletions, order creation and product creation require confirm: true and an idempotency_key. A replayed key returns the original result with idempotent_replay: true.
  • Prices are integer minor units with an explicit currency. Sizes are centimetres.
  • Start from list_customisers to get an integer customiser id. Every other customiser tool needs one. Read an option family with list_customiser_options before writing to it.

Errors

  • 401 The response carries a resource_metadata challenge. No token, an expired token, or a token bound to another resource. Run discovery from the challenge URL and re-authorise.
  • invalid_target An authorization request whose resource parameter named an API other than this one. Send resource=https://web.signcustomiser.com/mcp, or omit it.
  • insufficient_scope A tool result, not a protocol error. The connection is valid; the merchant did not approve the permission that tool needs. Read required_scopes from the error and ask the merchant to reconnect and approve it. Do not retry.
  • -32602 An argument failed the tool's input schema. Read the argument name from the message and correct it.
  • 429 The endpoint's own rate limit. Wait for retry_after.

Reference

  • mcp-tools.json Every tool with its scope, annotations, input and output schema, error cases and wire-shape examples. One file, generated from the running server.
  • /help/mcp/ The tool reference. One page per tool at /help/mcp/tools/<tool_name>/, each with a .md alternate at the same path plus .md.
  • /help/mcp/guides/connect/ Per-client setup, what the merchant approves, and how a connection is revoked.
  • /help/mcp/guides/authentication/ Discovery, dynamic registration, PKCE, resource binding, token lifetimes, revocation.
  • /help/mcp/guides/advanced-catalogue/ search_operations and the four executors that reach the rest of the platform API under mcp:advanced.
  • /help/mcp/guides/code-mode/ Generating typed code against the tool schemas instead of calling tools one at a time.
  • /help/llms.txt The documentation index in plain text. /help/llms-full.txt is the whole corpus in one file.

Using an assistant rather than building one? The MCP server overview explains what a connection can do and how a merchant approves it.

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