Decisionmatrix MCP Server

DecisionMatrix MCP

A transparent, 100% deterministic Model Context Protocol (MCP) server that gives LLM agents a reliable multi-criteria decision analysis (MCDA) engine.

Agents are great at gathering options but unreliable at weighing them: they lose precision, apply inconsistent weights, and can't show their work. DecisionMatrix offloads the scoring to an exact, explainable engine. You provide options and weighted criteria (plus a score matrix); it returns a fully scored, ranked, and explained result — with per-criterion breakdowns, the methodology used, the weights applied, and a plain-language explanation.

Every number flows through decimal.js at 40-digit precision (never floats), so identical inputs always produce byte-identical output. The server is stateless — no database, no sessions.

🌐 Live hosted server (free, no install)

A public remote MCP server runs on Cloudflare's edge — point any Streamable-HTTP MCP client at it:

https://decisionmatrix-mcp.pages.dev/mcp

{ "mcpServers": { "decisionmatrix": {
    "type": "http", "url": "https://decisionmatrix-mcp.pages.dev/mcp" } } }

It runs in open mode on the free tier (no key, 15 calls/day per IP). Paid plans (Starter $12/mo · 5,000/day, Pro $39/mo · 50,000/day) are live via Stripe Checkout — buy a plan, get an API key instantly, and send it as X-API-Key. Self-host for unlimited calls with no keys. Landing page + pricing: https://decisionmatrix-mcp.pages.dev.

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What it does

Six tools, all returning a uniform, agent-parseable envelope:

Scoring methods

Each criterion has a direction: benefit (higher is better — quality, speed) or cost (lower is better — price, latency, risk). Weights are relative; they are normalized to sum to 1 internally.

Consistent response envelope

Every successful response contains: status, method, winner, ranking (with per-criterion breakdown), methodology, weights_used, inputs_used, notes, and a natural-language explanation.

{
  "status": "success",
  "method": "weighted_sum",
  "winner": { "option": "Gamma", "score": 0.666667, "score_exact": "0.666667", "rank": 1, "tie": false, "tied_with": [] },
  "ranking": [
    { "rank": 1, "option": "Gamma", "score": 0.666667, "score_exact": "0.666667",
      "breakdown": [
        { "criterion": "Price", "direction": "cost", "weight": 0.5, "weight_raw": "3",
          "raw_score": "900", "normalized_score": 1, "weighted_contribution": 0.5 }
      ] }
  ],
  "methodology": {
    "method": "weighted_sum",
    "name": "Weighted Sum Model (Simple Additive Weighting)",
    "normalization": "min-max per criterion (best value -> 1, worst -> 0)",
    "score_range": "0 to 1 (higher is better)",
    "weighting": "Criteria weights are normalized to sum to 1; only their relative sizes matter.",
    "deterministic": true
  },
  "weights_used": [ { "criterion": "Price", "direction": "cost", "weight_input": "3", "weight_normalized": 0.5 } ],
  "inputs_used": { "options": ["Alpha","Beta","Gamma"], "method": "weighted_sum", "option_count": 3, "criterion_count": 3 },
  "notes": [ "Scores are normalized within this option set; they express relative standing, not an absolute grade." ],
  "explanation": "Using the Weighted Sum Model, 'Gamma' ranks #1 with a score of 0.666667, ahead of 'Alpha' (0.527778) by 26.32% ..."
}

Errors never cross the tool boundary as exceptions — they come back as a structured, actionable envelope:

{
  "status": "error",
  "error": {
    "type": "incomplete_scores",
    "message": "Missing 1 score(s) in the options x criteria matrix.",
    "hint": "Provide a score for every option and criterion. Missing: Beta / Weight."
  }
}

Design note — exact numbers: score is a deterministically-rounded number (6 dp) for easy consumption; score_exact / raw_score are full-precision strings so no precision is lost in JSON. Rankings are computed on the exact values, with input order as a stable tie-break.

---

Project structure

decisionmatrix-mcp/
├── worker-src/
│   ├── index.mjs        # Cloudflare Pages Function (_worker.js): MCP over Streamable HTTP + billing routes
│   ├── engine.mjs       # The deterministic MCDA engine: 3 methods + 6 tools + validation
│   └── billing.mjs      # Stripe Checkout + KV-backed API keys, quota metering, webhook
├── site/
│   ├── index.html       # Static landing / pricing / docs page
│   └── _worker.js        # Built bundle (esbuild output; git-ignored)
├── tests/
│   └── engine.test.mjs  # 21 core scoring-logic tests (node --test)
├── examples/
│   └── agent_example.mjs # End-to-end MCP client demo over HTTP
├── package.json         # build / deploy / dev / test scripts
├── wrangler.toml        # Cloudflare Pages config
├── .env.example         # Optional auth/rate-limit env reference
├── LICENSE              # MIT
└── README.md

Separation of concerns: engine.mjs is pure and transport-agnostic (import it directly in tests or any Node/Deno/edge runtime); index.mjs only handles the MCP JSON-RPC wiring, HTTP, CORS, and the auth/metering seam.

---

Requirements

• Node 18+ (for the build, tests, and local dev). Only two dev/runtime deps: decimal.js (math) and esbuild (bundler).
• A Cloudflare account (free tier is fine) to deploy the hosted version.

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Run it locally

git clone <your-fork> decisionmatrix-mcp && cd decisionmatrix-mcp
npm install

# Run the test suite (no server needed)
npm test

# Serve the MCP endpoint locally via Wrangler (builds + runs Pages dev)
npm run dev          # -> http://127.0.0.1:8788/mcp

# Try the end-to-end client demo (hosted by default, or pass a local URL)
node examples/agent_example.mjs
node examples/agent_example.mjs http://127.0.0.1:8788

Quick manual call:

curl -s http://127.0.0.1:8788/mcp \
  -H 'content-type: application/json' \
  -H 'accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{
        "name":"list_methods","arguments":{}}}'

---

Client configuration

Cursor — ~/.cursor/mcp.json

{ "mcpServers": { "decisionmatrix": {
    "url": "https://decisionmatrix-mcp.pages.dev/mcp" } } }

Claude Desktop — claude_desktop_config.json

Claude Desktop launches stdio servers, so bridge to the HTTP endpoint with mcp-remote:

{ "mcpServers": { "decisionmatrix": {
    "command": "npx", "args": ["-y", "mcp-remote", "https://decisionmatrix-mcp.pages.dev/mcp"] } } }

VS Code — .vscode/mcp.json

{ "servers": { "decisionmatrix": {
    "type": "http", "url": "https://decisionmatrix-mcp.pages.dev/mcp" } } }

Any Streamable-HTTP MCP client

Point it at https://decisionmatrix-mcp.pages.dev/mcp (or your self-hosted URL). If you enable auth, add X-API-Key (or Authorization: Bearer <key>) in the client's headers.

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Tools & parameters

create_decision(options, criteria, scores, method="weighted_sum")

• options — array of names (["Vendor A","Vendor B"]) or objects ([{"name":"Vendor A","scores":{...}}]). Minimum 2, names unique.
• criteria — array of { "name", "weight" (>=0), "direction": "benefit"|"cost" }. At least one weight must be > 0.
• scores — the option×criterion matrix. Accepted shapes:
  • object map: { "Vendor A": { "Price": 100, "Quality": 8 }, ... }
  • array: [ { "option": "Vendor A", "scores": { ... } }, ... ]
  • inline on each option object.
• method — weighted_sum (default) · weighted_product · topsis (aliases like saw, wpm, ideal also resolve).

score_options(options, criteria, scores, method)

Same inputs as create_decision; returns the full scored matrix (per-option, per-criterion normalized scores + totals) without the winner narrative.

sensitivity_analysis(options, criteria, scores, method, variation=0.2, steps=10)

Sweeps each criterion's weight from -variation to +variation (fractional, e.g. 0.2 = ±20%) in steps increments (2–100), renormalizing the others, and recomputes the winner each time. Returns a robustness_score (share of scenarios the baseline winner stays #1), the fragile_criteria, and per-criterion flip points.

compare_two(option_a, option_b, criteria, scores, method)

Head-to-head between exactly two options (pass option_a/option_b names, or a 2-element options array). Returns the winner, score margin, criteria_wins, and a per_criterion breakdown showing which option each criterion favours.

list_methods() / health_check()

Discovery + status. No parameters.

---

Example tool-call payloads

Choose a laptop (price & weight are cost criteria):

{ "name": "create_decision", "arguments": {
  "options": ["Alpha", "Beta", "Gamma"],
  "criteria": [
    { "name": "Price",   "weight": 3, "direction": "cost" },
    { "name": "Battery", "weight": 2, "direction": "benefit" },
    { "name": "Weight",  "weight": 1, "direction": "cost" }
  ],
  "scores": {
    "Alpha": { "Price": 1000, "Battery": 8,  "Weight": 1.5 },
    "Beta":  { "Price": 1200, "Battery": 12, "Weight": 1.8 },
    "Gamma": { "Price": 900,  "Battery": 6,  "Weight": 1.2 }
  }
} }

Test how robust the winner is:

{ "name": "sensitivity_analysis", "arguments": {
  "options": ["Alpha", "Beta", "Gamma"],
  "criteria": [
    { "name": "Price", "weight": 3, "direction": "cost" },
    { "name": "Battery", "weight": 2 }
  ],
  "scores": { "Alpha": {"Price":1000,"Battery":8}, "Beta": {"Price":1200,"Battery":12}, "Gamma": {"Price":900,"Battery":6} },
  "variation": 0.3, "steps": 8
} }

Head-to-head:

{ "name": "compare_two", "arguments": {
  "option_a": "Alpha", "option_b": "Beta",
  "criteria": [ { "name": "Price", "weight": 3, "direction": "cost" }, { "name": "Battery", "weight": 2 } ],
  "scores": { "Alpha": {"Price":1000,"Battery":8}, "Beta": {"Price":1200,"Battery":12} }
} }

---

Deploy on Cloudflare Pages

Same pattern as PrecisionCalc — one build step bundles worker-src/ into site/_worker.js (Pages "advanced mode" Function), then Wrangler deploys the site/ directory.

npm install
npx wrangler login          # once

# Build + deploy in one shot
npm run deploy              # esbuild -> site/_worker.js, then wrangler pages deploy

Or wire it to Git: create a Pages project, set the build command to npm run build and the output directory to site. Every push deploys automatically. The compatibility_date and project name live in wrangler.toml.

To run fully free / private, you need no bindings, secrets, or env vars — the scoring engine is stateless and the server fails open (free tier, quota disabled).

Enabling billing (already live on the hosted server)

The hosted server uses these — replicate them for your own paid deployment:

1. KV namespace for API keys + daily usage counters, bound as DECISIONMATRIX_KV in wrangler.toml.
2. Stripe products/prices (subscription) — put the price IDs in [vars] (PRICE_STARTER, PRICE_PRO) and the daily limits (FREE_DAILY, STARTER_DAILY, PRO_DAILY).
3. Stripe secrets (never in the repo):

   wrangler pages secret put STRIPE_SECRET_KEY     --project-name decisionmatrix-mcp
   wrangler pages secret put STRIPE_WEBHOOK_SECRET  --project-name decisionmatrix-mcp
   

4. Webhook → create a Stripe webhook endpoint at https://<your-domain>/webhook for customer.subscription.updated + customer.subscription.deleted.

Routes wired up: /checkout?plan=starter|pro → Stripe Checkout, /success provisions and shows the API key (idempotent), /portal opens the Stripe billing portal, /webhook handles subscription lifecycle (revoke/restore), /metrics reports usage.

---

Auth & rate limiting

The hosted server enforces tiered quotas in worker-src/billing.mjs:

• Identity — identify() reads X-API-Key / Authorization: Bearer, looks the key up in KV, and falls back to per-IP free tier.
• Quota — consumeQuota() is a KV daily counter (resets 00:00 UTC); the single gating point in handleRpc where method === "tools/call".
• Paywall response — over-quota / invalid / revoked keys get a structured upsell envelope with pricing + checkout URLs (agents can read and act on it).
• Usage metering — in-memory counters at /metrics.

DecisionMatrix has no paid-only tools — every tool works on every tier; paid plans only raise the daily quota. To make a tool paid-only, add its name to PAID_ONLY_TOOLS in index.mjs. Because the engine is pure and stateless, none of this touches the scoring logic.

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Design decisions & assumptions

• Deterministic by construction. 40-digit decimal math, ROUND_HALF_UP everywhere, and stable input-order tie-breaking. No floats, no randomness, no clocks in the result.
• Normalization is per-criterion and direction-aware. weighted_sum uses min-max (best→1, worst→0); if a criterion is identical across all options it's treated as neutral (normalized to 1) and noted. weighted_product uses ratio normalization and requires strictly positive scores (clear error otherwise). topsis uses vector normalization and ranks by closeness to the ideal/anti-ideal.
• Weights are relative — normalized to sum to 1, so [3,2,1] and [30,20,10] give identical results.
• Scores are relative to the option set — they measure standing within the provided alternatives, not an absolute grade. This is stated in notes.
• Errors are data, not exceptions — every tool returns status:"error" with a machine type and an actionable hint. Validation covers duplicate names, missing cells (listing exactly which), non-numeric scores, bad weights/directions, and unknown methods.
• Stateless & side-effect-free — trivially cacheable, horizontally scalable, and safe to run anywhere (Cloudflare, Node, Deno, Bun).

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Testing

npm test          # node --test tests/*.test.mjs  (21 tests, no network)

The suite pins the hand-verifiable weighted_sum arithmetic, checks determinism, weight-relativity, direction handling, ties, all three methods, compare_two, sensitivity_analysis, the multiple score-input shapes, and every error path.

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Roadmap (post-MVP)

1. More methods: AHP (pairwise weight elicitation), ELECTRE, PROMETHEE, Borda count.
2. Group decisions: aggregate multiple stakeholders' weight/score sets.
3. Monte-Carlo sensitivity (perturb all weights jointly) alongside one-at-a-time.
4. Per-key usage dashboard + Redis/Durable-Object quotas for stronger consistency.
5. Published npm package + a hosted multi-tenant tier.

License

MIT — see LICENSE.