diff --git a/.gitignore b/.gitignore
index 8c3f66c..875b2df 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,6 @@ npm-debug.log*
 
 # Per-session runtime locks (scheduled_tasks, etc.)
 .claude/*.lock
+
+# Local tooling env (developer-specific MCP endpoints/tokens)
+tools/.env
diff --git a/tools/README.md b/tools/README.md
new file mode 100644
index 0000000..431b2e4
--- /dev/null
+++ b/tools/README.md
@@ -0,0 +1,57 @@
+# EVOLV tooling (`tools/`)
+
+Repo-local tools and MCP services for EVOLV development. All Node.js
+native (no Python toolchain). Each tool encodes a rule that we've
+previously discovered through a bug; skipping them re-opens those bugs.
+
+See `CLAUDE.md` § "Tooling (Docker-first, local now, central later)"
+for the operating doctrine.
+
+## Tools (CLI)
+
+| Tool | Path | What it does | Run |
+|---|---|---|---|
+| `contract-verify` | `tools/contract-verify/` | Diffs `nodes/<n>/CONTRACT.md` topic table vs `src/commands/index.js` | `node tools/contract-verify/bin/contract-verify.js` |
+| `flow-lint` | `tools/flow-lint/` | Lints `examples/*.flow.json` against the flow-layout rule | `node tools/flow-lint/bin/flow-lint.js` |
+| `wiki-gen` | `tools/wiki-gen/` | Regenerates AUTOGEN topic-contract blocks in per-node wikis | `node tools/wiki-gen/bin/wiki-gen.js` |
+| `output-manifest-verify` | `tools/output-manifest-verify/` | Enforces the output-coverage manifest rule | `node tools/output-manifest-verify/bin/output-manifest-verify.js` |
+| `physics-sanity` | `tools/physics-sanity/` | Library of cross-node balance helpers; import from tests | `require('../../tools/physics-sanity')` |
+
+CI-friendly: every tool accepts `--json` (JSON output) and exits non-zero
+on findings.
+
+## MCP services (Docker)
+
+See `tools/mcp/README.md`. Three services scaffolded:
+
+| Service | Purpose | Status |
+|---|---|---|
+| `mcp-node-red-admin` | Wraps Node-RED admin HTTP API | TODO (scaffold) |
+| `mcp-influxdb` | Telemetry query + assertion | TODO (scaffold) |
+| `mcp-browser` | Headless Playwright against the dashboard | TODO (scaffold) |
+
+Start (once impls land):
+```bash
+cd tools && docker compose --profile mcp up -d
+```
+
+## CI integration
+
+Recommended order on every PR:
+
+```bash
+node tools/contract-verify/bin/contract-verify.js          # 1. CONTRACT vs registry
+node tools/flow-lint/bin/flow-lint.js                       # 2. Flow JSON shapes
+node tools/wiki-gen/bin/wiki-gen.js --check                  # 3. Wiki AUTOGEN blocks
+node tools/output-manifest-verify/bin/output-manifest-verify.js  # 4. Manifest coverage
+```
+
+Each is fast (<1 s on the whole repo).
+
+## Adding a new tool
+
+1. `tools/<name>/package.json` with a `bin` entry.
+2. `tools/<name>/bin/<name>.js` — must accept `--json` and exit 1 on drift.
+3. `tools/<name>/README.md` — one-page docs.
+4. Add a row to this README + a row to `CLAUDE.md` § Tooling.
+5. Wire into the CI snippet above.
diff --git a/tools/docker-compose.yml b/tools/docker-compose.yml
new file mode 100644
index 0000000..f1f37f4
--- /dev/null
+++ b/tools/docker-compose.yml
@@ -0,0 +1,46 @@
+name: evolv-tools
+
+services:
+  # ----------------------------------------------------------------------
+  # Local MCP services for the Claude Code tooling stack.
+  # Migration note (2026-05): these are deliberately local. When the
+  # central MCP server comes online (target Q3 2026), each service moves
+  # to the shared infra; this compose file becomes the spec for what to
+  # provision there. The build context + Dockerfile in tools/mcp/<name>/
+  # stays in this repo as the canonical definition.
+  # ----------------------------------------------------------------------
+
+  mcp-node-red-admin:
+    build:
+      context: ./mcp/node-red-admin
+    container_name: evolv-mcp-node-red-admin
+    environment:
+      NODE_RED_HOST: ${NODE_RED_HOST:-http://host.docker.internal:1880}
+      NODE_RED_TOKEN: ${NODE_RED_TOKEN:-}
+    stdin_open: true
+    tty: true
+    profiles: ["mcp"]
+
+  mcp-influxdb:
+    build:
+      context: ./mcp/influxdb
+    container_name: evolv-mcp-influxdb
+    environment:
+      INFLUX_URL: ${INFLUX_URL:-http://host.docker.internal:8086}
+      INFLUX_TOKEN: ${INFLUX_TOKEN:-}
+      INFLUX_ORG: ${INFLUX_ORG:-wbd}
+      INFLUX_BUCKET: ${INFLUX_BUCKET:-telemetry}
+    stdin_open: true
+    tty: true
+    profiles: ["mcp"]
+
+  mcp-browser:
+    build:
+      context: ./mcp/browser
+    container_name: evolv-mcp-browser
+    environment:
+      DASHBOARD_URL: ${DASHBOARD_URL:-http://host.docker.internal:1880/dashboard}
+      HEADLESS: ${HEADLESS:-true}
+    stdin_open: true
+    tty: true
+    profiles: ["mcp"]
diff --git a/tools/mcp/README.md b/tools/mcp/README.md
new file mode 100644
index 0000000..dd8f606
--- /dev/null
+++ b/tools/mcp/README.md
@@ -0,0 +1,97 @@
+# EVOLV MCP services — Docker stack
+
+Three MCP services Claude Code uses to close real loops during EVOLV work:
+
+| Service | What it does | Tools exposed |
+|---|---|---|
+| `mcp-node-red-admin` | Wraps the Node-RED HTTP admin API | `getFlows`, `postFlow`, `getFlow`, `inject`, `listNodes`, `restartFlow` |
+| `mcp-influxdb` | Queries the telemetry bucket | `query`, `assertSeriesExists`, `assertRecentWrite`, `listMeasurements` |
+| `mcp-browser` | Headless Playwright against the FlowFuse dashboard | `loadDashboard`, `screenshot`, `consoleLogs`, `waitForChart`, `getChartData` |
+
+## Why these
+
+Each closes a verification loop Claude currently cannot close:
+
+- **Node-RED admin** — today Claude pushes flows via raw `curl`; the
+  MCP lets Claude deploy + fire injects + read live state in one
+  conversational turn.
+- **InfluxDB** — today Claude cannot verify "did the telemetry land?"
+  beyond reading source. The MCP closes the loop after a deploy.
+- **Browser** — today Claude cannot see the rendered dashboard. The
+  MCP catches the failure mode behind the η-null crash + the
+  blank-ui-chart bug + the editor pile-up bug at the only layer where
+  they're visible.
+
+## Migration plan
+
+These run locally **now** (we're in the middle of an infra migration).
+Once the central MCP server is provisioned (target Q3 2026), each
+service moves to shared infra by lifting the entry from this
+`docker-compose.yml` plus the matching `tools/mcp/<name>/Dockerfile`
+and pointing every developer's Claude Code at the central endpoint
+instead of `localhost`. **The compose file stays here as the canonical
+definition.**
+
+## Usage
+
+```bash
+# build the three images (one-off, ~3 min)
+cd tools
+docker compose --profile mcp build
+
+# start them
+docker compose --profile mcp up -d
+
+# wire Claude Code to them — add to your user-level .mcp.json
+{
+  "mcpServers": {
+    "evolv-node-red-admin": { "type": "stdio", "command": "docker", "args": ["exec", "-i", "evolv-mcp-node-red-admin", "node", "server.mjs"] },
+    "evolv-influxdb":       { "type": "stdio", "command": "docker", "args": ["exec", "-i", "evolv-mcp-influxdb",       "node", "server.mjs"] },
+    "evolv-browser":        { "type": "stdio", "command": "docker", "args": ["exec", "-i", "evolv-mcp-browser",        "node", "server.mjs"] }
+  }
+}
+```
+
+The repo-level `.mcp.json` is deliberately **not** committed (each
+developer has different host endpoints / tokens). Use a user-level
+config or `~/.claude.json`.
+
+## Required environment
+
+`tools/.env` (gitignored) with:
+
+```dotenv
+NODE_RED_HOST=http://host.docker.internal:1880
+NODE_RED_TOKEN=…           # optional, only if Node-RED has admin auth on
+INFLUX_URL=http://host.docker.internal:8086
+INFLUX_TOKEN=…
+INFLUX_ORG=wbd
+INFLUX_BUCKET=telemetry
+DASHBOARD_URL=http://host.docker.internal:1880/dashboard
+```
+
+## Status
+
+| Service | Dockerfile | Server impl | Status |
+|---|---|---|---|
+| `mcp-node-red-admin` | placeholder | **TODO** — see `mcp/node-red-admin/ROADMAP.md` | not runnable yet |
+| `mcp-influxdb` | placeholder | **TODO** | not runnable yet |
+| `mcp-browser` | placeholder | **TODO** — wrap `@playwright/test` | not runnable yet |
+
+The compose file is the **target shape**. The Dockerfile + server
+implementation per service is a follow-up (each is ~200–400 LOC of MCP
+protocol + the wrapped client). When a service lands, flip its row
+above to `runnable` and remove the placeholder.
+
+## When to use these — required reading
+
+`CLAUDE.md` § "Tooling (Docker-first, local now, central later)" lists
+the operating doctrine: **always prefer these tools over ad-hoc
+curl/grep/manual checks**. Each tool exists because of a specific bug
+class we've already paid for. Skipping them re-opens those bugs.
+
+## Future: OPC-UA / PLC MCP
+
+Out of scope for this round; will be revisited later. When added it
+follows the same pattern: `tools/mcp/opcua/` with its own Dockerfile
+and a row in this README.
diff --git a/tools/mcp/browser/Dockerfile b/tools/mcp/browser/Dockerfile
new file mode 100644
index 0000000..1d858bc
--- /dev/null
+++ b/tools/mcp/browser/Dockerfile
@@ -0,0 +1,5 @@
+# placeholder — see ../README.md status table
+FROM node:20-alpine
+WORKDIR /app
+RUN echo 'console.error("mcp-browser not yet implemented"); process.exit(1);' > server.mjs
+CMD ["node", "server.mjs"]
diff --git a/tools/mcp/influxdb/Dockerfile b/tools/mcp/influxdb/Dockerfile
new file mode 100644
index 0000000..ea409c2
--- /dev/null
+++ b/tools/mcp/influxdb/Dockerfile
@@ -0,0 +1,5 @@
+# placeholder — see ../README.md status table
+FROM node:20-alpine
+WORKDIR /app
+RUN echo 'console.error("mcp-influxdb not yet implemented"); process.exit(1);' > server.mjs
+CMD ["node", "server.mjs"]
diff --git a/tools/mcp/node-red-admin/Dockerfile b/tools/mcp/node-red-admin/Dockerfile
new file mode 100644
index 0000000..6e01c4c
--- /dev/null
+++ b/tools/mcp/node-red-admin/Dockerfile
@@ -0,0 +1,5 @@
+# placeholder — see ROADMAP.md
+FROM node:20-alpine
+WORKDIR /app
+RUN echo 'console.error("mcp-node-red-admin not yet implemented — see ROADMAP.md"); process.exit(1);' > server.mjs
+CMD ["node", "server.mjs"]
diff --git a/tools/mcp/node-red-admin/ROADMAP.md b/tools/mcp/node-red-admin/ROADMAP.md
new file mode 100644
index 0000000..27fb53d
--- /dev/null
+++ b/tools/mcp/node-red-admin/ROADMAP.md
@@ -0,0 +1,50 @@
+# mcp-node-red-admin — implementation roadmap
+
+Status: placeholder. Compose entry exists, server impl is TODO.
+
+## Goal
+
+An MCP stdio server that wraps the Node-RED admin HTTP API, exposing the
+following tools to Claude Code:
+
+| Tool | Wraps | Use case |
+|---|---|---|
+| `node_red_get_flows` | `GET /flows` | Read deployed flow JSON |
+| `node_red_post_flow` | `POST /flow/:id` (single tab) | Deploy one tab without nuking others |
+| `node_red_replace_flows` | `POST /flows` (bulk) | Replace the entire flow set |
+| `node_red_inject` | `POST /inject/:nodeId` | Fire an inject node by id |
+| `node_red_list_nodes` | `GET /nodes` | Discover registered node types |
+| `node_red_restart_flow` | `DELETE` + redeploy | Force a restart of one tab |
+
+## Sketch
+
+```js
+// tools/mcp/node-red-admin/server.mjs
+import { Server } from '@modelcontextprotocol/sdk/server/index.js';
+import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
+
+const NODE_RED_HOST = process.env.NODE_RED_HOST;
+const TOKEN = process.env.NODE_RED_TOKEN;
+
+const server = new Server({ name: 'evolv-node-red-admin', version: '0.1.0' }, { capabilities: { tools: {} } });
+server.setRequestHandler(/* listTools */);
+server.setRequestHandler(/* callTool — fetch NODE_RED_HOST + tool's endpoint */);
+await server.connect(new StdioServerTransport());
+```
+
+## Dockerfile sketch
+
+```dockerfile
+FROM node:20-alpine
+WORKDIR /app
+COPY package.json server.mjs ./
+RUN npm install
+CMD ["node", "server.mjs"]
+```
+
+## When to build it
+
+After we've shipped enough EVOLV flow work that "deploy + fire inject +
+read state in one turn" becomes the dominant inner loop. Today the
+`curl` pattern still works for one-off deploys; the MCP earns its
+keep when the loop runs 5+ times per session.
diff --git a/tools/physics-sanity/README.md b/tools/physics-sanity/README.md
new file mode 100644
index 0000000..7e64207
--- /dev/null
+++ b/tools/physics-sanity/README.md
@@ -0,0 +1,80 @@
+# @evolv/physics-sanity
+
+Cross-node physical-balance helpers. Import from any node's test files
+to assert that scenario states close mass, hydraulic, hydraulic-power,
+oxygen-transfer, or energy balances within a stated tolerance.
+
+## Why
+
+Per-node unit tests verify shape and behaviour. They don't catch
+physically impossible plant states that arise from cross-node coupling
+— e.g. a pumpingStation reporting outflow > inflow + accumulation, or a
+diffuser reporting OTR inconsistent with its KLa × ΔC × V.
+
+These helpers don't replace per-node tests. They sit on top of an
+integration scenario and assert the closing balance.
+
+## Usage
+
+```js
+const sanity = require('../../../tools/physics-sanity');
+
+test('three-pump station closes the hydraulic balance', () => {
+  // … drive the scenario, take a snapshot …
+  const r = sanity.assertHydraulicBalance({
+    headerSuctionPa: ps.suctionPressurePa,
+    headerDischargePa: ps.dischargePressurePa,
+    pumpHeadPa: sumOfPumpHeads,
+    frictionPa: pipeFrictionEstimate,
+  });
+  assert.equal(r.ok, true, sanity.reportToString(r));
+});
+```
+
+## Helpers exported
+
+| Function | Asserts |
+|---|---|
+| `assertMassBalance({ inflowKgPerS, outflowKgPerS, accumulationKgPerS })` | `in - out - accumulation ≈ 0` |
+| `assertHydraulicBalance({ headerSuctionPa, headerDischargePa, pumpHeadPa, frictionPa, staticHeadPa })` | `ΔP_headers ≈ pumpHead - friction - static` |
+| `assertHydraulicPower({ flowM3PerS, headPa, shaftPowerW, efficiency })` | `shaft ≈ Q·H / η` |
+| `assertOxygenTransfer({ klaPerS, csMgPerL, cMgPerL, otrKgPerS, volumeM3 })` | `OTR ≈ KLa · (Cs - C) · V` |
+| `assertEnergyBalance({ heatInW, workInW, heatOutW, workOutW, accumulationW })` | `Q_in + W_in ≈ Q_out + W_out + ΔE` |
+
+Each returns `{ ok, label, ...residuals }`. `reportToString(r)` formats
+for human-readable failure messages.
+
+## CLI demo
+
+```bash
+node tools/physics-sanity/bin/physics-sanity.js
+```
+
+Runs four sanity-check scenarios against the helpers (smoke-test for
+the library itself).
+
+## Tolerance defaults
+
+| Domain | Absolute | Relative |
+|---|---|---|
+| mass | 1e-6 kg/s | 0.1 % |
+| hydraulic ΔP | 50 Pa (0.5 mbar) | 0.1 % |
+| hydraulic power | 1 W | 0.5 % |
+| OTR | 1e-4 kg/s | 0.5 % |
+| energy | 1 W | 0.1 % |
+
+Override per call with `absTol` / `relTol`.
+
+## Where to use this
+
+Out-of-the-box destinations:
+
+| Scenario | Where to add | Calls |
+|---|---|---|
+| pumpingStation hydraulic closure | `nodes/pumpingStation/test/integration/` | `assertHydraulicBalance`, `assertHydraulicPower` |
+| reactor → settler mass balance | `nodes/reactor/test/integration/` | `assertMassBalance` |
+| diffuser OTR vs reactor uptake | `nodes/diffuser/test/integration/` | `assertOxygenTransfer` |
+| machineGroupControl efficiency sanity | `nodes/machineGroupControl/test/integration/` | `assertHydraulicPower` |
+
+A future tool can scan integration tests and report which scenarios do
+or don't have a closing-balance assertion.
diff --git a/tools/physics-sanity/bin/physics-sanity.js b/tools/physics-sanity/bin/physics-sanity.js
new file mode 100644
index 0000000..4ca9a54
--- /dev/null
+++ b/tools/physics-sanity/bin/physics-sanity.js
@@ -0,0 +1,18 @@
+#!/usr/bin/env node
+'use strict';
+
+const lib = require('../index.js');
+
+function runDemo() {
+  const checks = [
+    lib.assertMassBalance({ inflowKgPerS: 12.5, outflowKgPerS: 12.5, accumulationKgPerS: 0, label: 'reactor-passthrough' }),
+    lib.assertHydraulicBalance({ headerSuctionPa: 0, headerDischargePa: 110000, pumpHeadPa: 110000, label: 'station-A-headers' }),
+    lib.assertHydraulicPower({ flowM3PerS: 0.030, headPa: 110000, shaftPowerW: 5000, efficiency: 0.66, label: 'pump-A' }),
+    lib.assertOxygenTransfer({ klaPerS: 0.002, csMgPerL: 9.0, cMgPerL: 2.0, otrKgPerS: 2.8e-7, volumeM3: 20, label: 'diffuser-A' }),
+  ];
+  for (const c of checks) process.stdout.write(lib.reportToString(c) + '\n');
+  const failed = checks.filter((c) => !c.ok).length;
+  process.exit(failed > 0 ? 1 : 0);
+}
+
+if (require.main === module) runDemo();
diff --git a/tools/physics-sanity/index.js b/tools/physics-sanity/index.js
new file mode 100644
index 0000000..82ba32a
--- /dev/null
+++ b/tools/physics-sanity/index.js
@@ -0,0 +1,111 @@
+'use strict';
+
+const PA_PER_MBAR = 100;
+const SECONDS_PER_HOUR = 3600;
+
+function withinTolerance(observed, expected, absTol, relTol) {
+  if (!Number.isFinite(observed) || !Number.isFinite(expected)) return false;
+  const absErr = Math.abs(observed - expected);
+  if (absErr <= absTol) return true;
+  if (Math.abs(expected) > 0) return absErr / Math.abs(expected) <= relTol;
+  return false;
+}
+
+function assertMassBalance({ inflowKgPerS, outflowKgPerS, accumulationKgPerS = 0, label = 'mass', absTol = 1e-6, relTol = 1e-3 } = {}) {
+  const expected = inflowKgPerS - accumulationKgPerS;
+  const ok = withinTolerance(outflowKgPerS, expected, absTol, relTol);
+  return {
+    ok,
+    label,
+    inflowKgPerS,
+    outflowKgPerS,
+    accumulationKgPerS,
+    residualKgPerS: inflowKgPerS - outflowKgPerS - accumulationKgPerS,
+    relErr: expected === 0 ? null : (outflowKgPerS - expected) / expected,
+  };
+}
+
+function assertHydraulicBalance({ headerSuctionPa, headerDischargePa, pumpHeadPa, frictionPa = 0, staticHeadPa = 0, label = 'hydraulic', absTol = 50, relTol = 1e-3 } = {}) {
+  const lhs = headerDischargePa - headerSuctionPa;
+  const rhs = pumpHeadPa - frictionPa - staticHeadPa;
+  const ok = withinTolerance(lhs, rhs, absTol, relTol);
+  return {
+    ok,
+    label,
+    lhsPa: lhs,
+    rhsPa: rhs,
+    residualPa: lhs - rhs,
+    residualMbar: (lhs - rhs) / PA_PER_MBAR,
+  };
+}
+
+function assertHydraulicPower({ flowM3PerS, headPa, shaftPowerW, efficiency, label = 'hydraulic-power', absTol = 1, relTol = 5e-3 } = {}) {
+  if (!Number.isFinite(efficiency) || efficiency <= 0 || efficiency > 1.0) {
+    return { ok: false, label, msg: `efficiency=${efficiency} outside (0,1]` };
+  }
+  const expectedShaftPowerW = (flowM3PerS * headPa) / efficiency;
+  const ok = withinTolerance(shaftPowerW, expectedShaftPowerW, absTol, relTol);
+  return {
+    ok,
+    label,
+    flowM3PerS,
+    headPa,
+    efficiency,
+    expectedShaftPowerW,
+    observedShaftPowerW: shaftPowerW,
+    residualW: shaftPowerW - expectedShaftPowerW,
+  };
+}
+
+function assertEnergyBalance({ heatInW = 0, workInW = 0, heatOutW = 0, workOutW = 0, accumulationW = 0, label = 'energy', absTol = 1, relTol = 1e-3 } = {}) {
+  const inputs = heatInW + workInW;
+  const outputs = heatOutW + workOutW + accumulationW;
+  const ok = withinTolerance(inputs, outputs, absTol, relTol);
+  return {
+    ok,
+    label,
+    inputsW: inputs,
+    outputsW: outputs,
+    residualW: inputs - outputs,
+  };
+}
+
+function assertOxygenTransfer({ klaPerS, csMgPerL, cMgPerL, otrKgPerS, volumeM3, label = 'OTR', absTol = 1e-4, relTol = 5e-3 } = {}) {
+  if (!Number.isFinite(klaPerS) || klaPerS < 0) return { ok: false, label, msg: `KLa=${klaPerS} invalid` };
+  if (!Number.isFinite(volumeM3) || volumeM3 <= 0) return { ok: false, label, msg: `volume=${volumeM3} invalid` };
+  const driveMgPerL = csMgPerL - cMgPerL;
+  const expectedKgPerS = klaPerS * driveMgPerL * volumeM3 * 1e-3 / SECONDS_PER_HOUR * SECONDS_PER_HOUR / 1000;
+  const expectedKgPerS_corrected = klaPerS * driveMgPerL * volumeM3 / 1e6;
+  const ok = withinTolerance(otrKgPerS, expectedKgPerS_corrected, absTol, relTol);
+  return {
+    ok,
+    label,
+    klaPerS,
+    csMgPerL,
+    cMgPerL,
+    driveMgPerL,
+    volumeM3,
+    expectedKgPerS: expectedKgPerS_corrected,
+    observedKgPerS: otrKgPerS,
+    residualKgPerS: otrKgPerS - expectedKgPerS_corrected,
+  };
+}
+
+function reportToString(r) {
+  if (r.ok) return `OK   ${r.label}`;
+  const fields = Object.entries(r)
+    .filter(([k]) => !['ok', 'label'].includes(k))
+    .map(([k, v]) => `${k}=${typeof v === 'number' ? v.toExponential(3) : v}`)
+    .join(' ');
+  return `FAIL ${r.label}  ${fields}`;
+}
+
+module.exports = {
+  assertMassBalance,
+  assertHydraulicBalance,
+  assertHydraulicPower,
+  assertEnergyBalance,
+  assertOxygenTransfer,
+  reportToString,
+  PA_PER_MBAR,
+};
diff --git a/tools/physics-sanity/package.json b/tools/physics-sanity/package.json
new file mode 100644
index 0000000..af462aa
--- /dev/null
+++ b/tools/physics-sanity/package.json
@@ -0,0 +1,14 @@
+{
+  "name": "@evolv/physics-sanity",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Cross-node physical-balance helpers (mass, hydraulic, energy). Import from test files; closure tolerance asserted at known plant states.",
+  "main": "index.js",
+  "bin": {
+    "evolv-physics-sanity": "bin/physics-sanity.js"
+  },
+  "scripts": {
+    "test": "node --test test/*.test.js"
+  },
+  "license": "UNLICENSED"
+}
diff --git a/tools/physics-sanity/test/balance.test.js b/tools/physics-sanity/test/balance.test.js
new file mode 100644
index 0000000..16ff51e
--- /dev/null
+++ b/tools/physics-sanity/test/balance.test.js
@@ -0,0 +1,57 @@
+'use strict';
+
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const lib = require('../index.js');
+
+test('mass balance closes for steady-state pass-through', () => {
+  const r = lib.assertMassBalance({ inflowKgPerS: 10, outflowKgPerS: 10 });
+  assert.equal(r.ok, true);
+  assert.equal(r.residualKgPerS, 0);
+});
+
+test('mass balance reports residual when leaking', () => {
+  const r = lib.assertMassBalance({ inflowKgPerS: 10, outflowKgPerS: 9.5 });
+  assert.equal(r.ok, false);
+  assert.equal(Math.round(r.residualKgPerS * 1000), 500);
+});
+
+test('hydraulic balance: ΔP = pumpHead - friction - static', () => {
+  const r = lib.assertHydraulicBalance({
+    headerSuctionPa: 0,
+    headerDischargePa: 90000,
+    pumpHeadPa: 100000,
+    frictionPa: 8000,
+    staticHeadPa: 2000,
+  });
+  assert.equal(r.ok, true);
+});
+
+test('hydraulic power Q·H / η — within 0.5% relative tolerance', () => {
+  const Q = 0.03;
+  const H = 100000;
+  const eta = 0.65;
+  const shaft = (Q * H) / eta;
+  const r = lib.assertHydraulicPower({ flowM3PerS: Q, headPa: H, shaftPowerW: shaft, efficiency: eta });
+  assert.equal(r.ok, true);
+});
+
+test('hydraulic power flags eta=0', () => {
+  const r = lib.assertHydraulicPower({ flowM3PerS: 0.03, headPa: 100000, shaftPowerW: 5000, efficiency: 0 });
+  assert.equal(r.ok, false);
+});
+
+test('OTR check uses standard KLa formula', () => {
+  const kla = 0.002;
+  const cs = 9.0;
+  const c = 2.0;
+  const V = 20;
+  const otr = kla * (cs - c) * V / 1e6;
+  const r = lib.assertOxygenTransfer({ klaPerS: kla, csMgPerL: cs, cMgPerL: c, volumeM3: V, otrKgPerS: otr });
+  assert.equal(r.ok, true);
+});
+
+test('energy balance: heat-in + work-in = heat-out + work-out + accumulation', () => {
+  const r = lib.assertEnergyBalance({ heatInW: 1000, workInW: 200, heatOutW: 700, workOutW: 400, accumulationW: 100 });
+  assert.equal(r.ok, true);
+});