PriorityMCP

An MCP server over a live Priority ERP installation. It gives an LLM the tools to find the right screen, learn what its columns mean, and query it — rather than a hard-coded method per business question.

Ten tools over Priority's OData v4 API, plus a second channel through priority-web-sdk for running Priority programs. Serves both transports: stdio for a local client, and Streamable HTTP over TLS so clients on other machines can connect.

Why discovery rather than a method per domain

The first version of this server had one curated tool, get_sales, built on a hand-coded map of four invoice screens. Building that map required guessing what each screen meant, and one of the guesses was wrong: CINVOICES was coded as "credit invoices" and its amounts multiplied by -1.

EFORM.TITLE on the server says חשבוניות מרכזות — consolidated invoices. Credit invoices are a different screen entirely (SALECREDITINVOICES, table CUSTSALES), and on that installation it is not exposed to the API at all. Every total produced from that mapping was wrong, and nothing in the output looked wrong. The database had held the correct answer the whole time, in a table nobody had queried.

So the design rule here is: the model asks Priority what things are. Screen names are opaque English codes whose meaning lives in a Hebrew title, and inferring one from the other is exactly the mistake to prevent. get_sales still exists but is hidden by default (PRIORITY_ENABLE_GET_SALES=1 to expose it) — when it is available the model reaches for it and never exercises discovery.

Related MCP server: MCP Server for Odoo

Quick start

Requires Node 20+. There is no build step: tsx runs the TypeScript directly, so the code in src/ is the code that runs.

npm install
copy .env.example .env      # then fill it in -- every field is documented in place
npm run probe               # verifies the connection and what Priority exposes
npm run server              # stdio, for a local MCP client

To serve other machines:

powershell -ExecutionPolicy Bypass -File scripts/make-cert.ps1   # prints the two .env lines
npm run server:http                                              # HTTPS on :3401
powershell -File scripts/client-kit.ps1                          # a folder to hand to each client

As a Windows service (WinSW), so it survives logout and reboot:

.\service\install-service.ps1     # as Administrator

The service runs src/http.ts from this directory, so deploying a change is Restart-Service PriorityMCP — no reinstall. Reinstall only when service/priority-mcp.xml itself changes. Run npm run typecheck before restarting: the service retries three times on failure and then stays down, so one syntax error is an outage.

The tools

Clients also receive ~3,100 characters of server-level instructions on initialize (the discovery order, case sensitivity, never summing currencies, how reversals work). You do not need to write a system prompt for this.

What was measured about this Priority server

These are findings from the live installation, not documentation. Each one shapes the code, and several are silent failures — the reason the tools do not simply forward OData:

The dictionary comes from EFORM (~5,800 forms) and is cached on disk for 24 hours, keyed per installation and shared across companies — screen definitions live at the tabula.ini level, so every company on one installation has the same dictionary.

Configuration

Everything is in .env, and every setting is documented where it is defined — see .env.example. The three that decide the shape of a deployment:

• PRIORITY_ODATA_URL + PRIORITY_ENVIRONMENTS — end the URL at the tabula.ini and list companies to let callers choose one; end it with a company name for a single-company server. The list is an allowlist, not a hint: the name goes into a URL path, so anything unlisted is refused.

• PRIORITY_AUTH_MODE — shared (one identity from .env), headers (each caller supplies its own), or elicit (the client asks its user). Header and elicited credentials never enter the model's context, which is why there is no login() tool.

• PRIORITY_READ_ONLY — 1 removes run_program, leaving no way to change anything. Discovery and read tools are never gated: without them a model cannot learn a screen name and goes back to inferring one, which is the failure above.

MCP_AUTH_TOKEN is required whenever the listener is not loopback-only. The server refuses to start without it rather than warning — it holds Priority credentials and every tool reads live ERP data.

Connecting a client

{
  "mcpServers": {
    "priority": {
      "type": "http",
      "url": "https://<server>:3401/mcp",
      "headers": {
        "X-Priority-User": "...",
        "X-Priority-Pass": "...",
        "X-Priority-Company": "demo"
      }
    }
  }
}

Or Authorization: Bearer <MCP_AUTH_TOKEN> to use the server's own identity. Header credentials require TLS and are refused over plain HTTP. scripts/client-kit.ps1 packages the CA and these templates into a folder to hand to each client machine.

On Windows, verifying with curl needs --ssl-revoke-best-effort: curl there uses schannel, which requires a revocation source, and a private CA publishes no CRL. The flag relaxes the revocation check only. Node-based clients do not need it.

Tests

npm run typecheck
npm test                          # 8 offline suites -- no server, no Priority
npm run test:live                 # 11 suites against the real installation
npx tsx tests/live.http.ts        # the HTTP transport, as a remote client
npx tsx tests/live.headerauth.ts  # all four accepted and four refused auth paths

Live tests need NODE_EXTRA_CA_CERTS=<repo>\certs\mcp-ca.pem when TLS is on.

A live suite that cannot reach a resource skips with a stated reason rather than passing quietly — a Priority permission that is closed must not read as a green test.

Layout

src/
  server.ts       tool registration, the model-facing instructions
  http.ts         Streamable HTTP transport, TLS, sessions, authentication
  odata.ts        the Priority OData client, EDMX parsing, the quirks above
  dictionary.ts   the EFORM screen dictionary, cache, Hebrew search
  discovery.ts    search_screens / describe_screen / query / column sources
  aggregate.ts    grouping and totals, computed here
  companies.ts    per-company context over one shared dictionary
  auth.ts         shared / headers / elicit
  help.ts         screen help from EXEC/FORMHELP, HTML and {XXXX.T} references
  programs.ts     the priority-web-sdk channel
service/          WinSW wrapper, install / uninstall
scripts/          make-cert.ps1, client-kit.ps1
tests/            *.test.ts offline, live.*.ts against the installation

node_modules is not in git (336 MB); package-lock.json is, so npm install restores what this was verified against. certs/, .env and service/priority-mcp.exe are also excluded — the repo alone does not reinstall the service.