diff --git a/.github/workflows/openapi-contract.yml b/.github/workflows/openapi-contract.yml
new file mode 100644
index 0000000..d6e2eca
--- /dev/null
+++ b/.github/workflows/openapi-contract.yml
@@ -0,0 +1,39 @@
+name: Validate OpenAPI contract
+
+on:
+  pull_request:
+    paths:
+      - "docs/openapi/**"
+      - "scripts/validate-openapi-contract.mjs"
+      - "scripts/test-openapi-contract.mjs"
+      - ".github/workflows/openapi-contract.yml"
+  push:
+    branches:
+      - main
+    paths:
+      - "docs/openapi/**"
+      - "scripts/validate-openapi-contract.mjs"
+      - "scripts/test-openapi-contract.mjs"
+      - ".github/workflows/openapi-contract.yml"
+
+permissions:
+  contents: read
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - name: Validate OpenAPI contract
+        run: node scripts/validate-openapi-contract.mjs
+
+      - name: Test contract validator
+        run: node scripts/test-openapi-contract.mjs
diff --git a/scripts/test-openapi-contract.mjs b/scripts/test-openapi-contract.mjs
new file mode 100644
index 0000000..6297e73
--- /dev/null
+++ b/scripts/test-openapi-contract.mjs
@@ -0,0 +1,91 @@
+#!/usr/bin/env node
+
+// Regression tests for scripts/validate-openapi-contract.mjs.
+// Runs the validator as a subprocess against the real spec and against
+// deliberately broken temp copies.
+
+import assert from "node:assert/strict";
+import { spawnSync } from "node:child_process";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import process from "node:process";
+import { fileURLToPath } from "node:url";
+
+const REPO_ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const VALIDATOR = path.join(REPO_ROOT, "scripts/validate-openapi-contract.mjs");
+const REAL_SPEC = path.join(REPO_ROOT, "docs/openapi/qveris-public-api.openapi.json");
+const tmpRoot = fs.mkdtempSync(path.join(os.tmpdir(), "qveris-openapi-contract-"));
+
+function run(specPath) {
+  return spawnSync(process.execPath, [VALIDATOR, specPath], { encoding: "utf8" });
+}
+
+function writeSpec(name, mutate) {
+  const spec = JSON.parse(fs.readFileSync(REAL_SPEC, "utf8"));
+  mutate(spec);
+  const target = path.join(tmpRoot, name);
+  fs.writeFileSync(target, JSON.stringify(spec));
+  return target;
+}
+
+const tests = [
+  ["accepts the real checked-in spec", () => {
+    const result = run(REAL_SPEC);
+    assert.equal(result.status, 0, result.stderr);
+    assert.match(result.stdout, /OpenAPI contract OK/);
+  }],
+  ["rejects a missing file", () => {
+    const result = run(path.join(tmpRoot, "does-not-exist.json"));
+    assert.equal(result.status, 1);
+    assert.match(result.stderr, /not found/);
+  }],
+  ["rejects invalid JSON", () => {
+    const target = path.join(tmpRoot, "broken.json");
+    fs.writeFileSync(target, "{ not json");
+    const result = run(target);
+    assert.equal(result.status, 1);
+    assert.match(result.stderr, /not valid JSON/);
+  }],
+  ["rejects valid JSON that is not an object", () => {
+    const target = path.join(tmpRoot, "null.json");
+    fs.writeFileSync(target, "null");
+    const result = run(target);
+    assert.equal(result.status, 1);
+    assert.match(result.stderr, /not a valid OpenAPI object/);
+  }],
+  ["rejects missing info.version", () => {
+    const target = writeSpec("no-version.json", (spec) => {
+      delete spec.info.version;
+    });
+    const result = run(target);
+    assert.equal(result.status, 1);
+    assert.match(result.stderr, /info\.version/);
+  }],
+  ["rejects a missing core path", () => {
+    const target = writeSpec("no-search.json", (spec) => {
+      delete spec.paths["/search"];
+    });
+    const result = run(target);
+    assert.equal(result.status, 1);
+    assert.match(result.stderr, /missing required path: \/search/);
+  }],
+  ["rejects a missing component schema", () => {
+    const target = writeSpec("no-schema.json", (spec) => {
+      delete spec.components.schemas.PublicSearchResponse;
+    });
+    const result = run(target);
+    assert.equal(result.status, 1);
+    assert.match(result.stderr, /missing required component schema: PublicSearchResponse/);
+  }],
+];
+
+try {
+  for (const [name, testFn] of tests) {
+    testFn();
+    console.log(`ok ${name}`);
+  }
+  console.log(`\n${tests.length} OpenAPI contract regression test(s) passed.`);
+} finally {
+  fs.rmSync(tmpRoot, { recursive: true, force: true });
+}
diff --git a/scripts/validate-openapi-contract.mjs b/scripts/validate-openapi-contract.mjs
new file mode 100644
index 0000000..36dcde8
--- /dev/null
+++ b/scripts/validate-openapi-contract.mjs
@@ -0,0 +1,120 @@
+#!/usr/bin/env node
+
+// Issue #37 Phase 1: validate the mirrored public OpenAPI contract.
+//
+// The website (qveris-website) owns the public REST contract and mirrors
+// docs/openapi/qveris-public-api.openapi.json into this repo. This script is
+// a zero-dependency drift check: it fails CI when the checked-in contract is
+// missing the version, the core paths, or the response schemas the toolkit
+// (CLI / MCP / Python SDK) depends on. It does NOT generate types — that is
+// Phase 2 of the issue and ships as a separate PR.
+
+import fs from "node:fs";
+import path from "node:path";
+import process from "node:process";
+import { fileURLToPath } from "node:url";
+
+const REPO_ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const DEFAULT_SPEC = path.join("docs", "openapi", "qveris-public-api.openapi.json");
+
+// Core agent-path endpoints the toolkit calls. Listed in the issue.
+const REQUIRED_PATHS = [
+  "/search",
+  "/tools/by-ids",
+  "/tools/execute",
+  "/auth/usage/history/v2",
+  "/auth/credits/ledger",
+];
+
+// Response/component schemas the toolkit clients deserialize. Keeping this
+// list intentionally focused on what the toolkit consumes so the check
+// catches contract drift without being brittle to unrelated backend schemas.
+const REQUIRED_SCHEMAS = [
+  "PublicSearchResponse",
+  "PublicCapabilityResult",
+  "PublicToolParameter",
+  "PublicToolStats",
+  "PublicBillingRule",
+  "PublicExecuteToolResponse",
+  "PublicCompactBillingStatement",
+  "APIResponse_UsageEventsResponse_",
+  "UsageEventsResponse",
+  "UsageEventItem",
+  "APIResponse_CreditsLedgerResponse_",
+  "CreditsLedgerResponse",
+  "CreditsLedgerItem",
+];
+
+function fail(errors) {
+  console.error("OpenAPI contract validation FAILED:");
+  for (const error of errors) console.error(`  - ${error}`);
+  console.error(
+    "\nThe public OpenAPI contract is mirrored from qveris-website. " +
+      "If this drift is intentional, re-mirror the spec; otherwise the backend contract changed."
+  );
+  process.exit(1);
+}
+
+function main() {
+  const specArg = process.argv[2];
+  const specPath = path.resolve(REPO_ROOT, specArg || DEFAULT_SPEC);
+  const rel = path.relative(REPO_ROOT, specPath);
+  const errors = [];
+
+  if (!fs.existsSync(specPath)) {
+    fail([`OpenAPI file not found: ${rel}`]);
+    return;
+  }
+
+  let spec;
+  try {
+    spec = JSON.parse(fs.readFileSync(specPath, "utf8"));
+  } catch (error) {
+    fail([`${rel} is not valid JSON: ${error.message}`]);
+    return;
+  }
+
+  if (!spec || typeof spec !== "object" || Array.isArray(spec)) {
+    fail([`${rel} is not a valid OpenAPI object`]);
+    return;
+  }
+
+  if (typeof spec.openapi !== "string" || !spec.openapi) {
+    errors.push("missing top-level `openapi` version string");
+  }
+
+  const infoVersion = spec.info && spec.info.version;
+  if (typeof infoVersion !== "string" || !infoVersion.trim()) {
+    errors.push("missing `info.version`");
+  }
+
+  const paths = spec.paths && typeof spec.paths === "object" ? spec.paths : {};
+  for (const required of REQUIRED_PATHS) {
+    if (!Object.prototype.hasOwnProperty.call(paths, required)) {
+      errors.push(`missing required path: ${required}`);
+    }
+  }
+
+  const schemas =
+    spec.components && spec.components.schemas && typeof spec.components.schemas === "object"
+      ? spec.components.schemas
+      : {};
+  for (const required of REQUIRED_SCHEMAS) {
+    if (!Object.prototype.hasOwnProperty.call(schemas, required)) {
+      errors.push(`missing required component schema: ${required}`);
+    }
+  }
+
+  if (errors.length > 0) {
+    fail(errors);
+    return;
+  }
+
+  console.log(`OpenAPI contract OK: ${rel}`);
+  console.log(`  openapi: ${spec.openapi}`);
+  console.log(`  info.version: ${infoVersion}`);
+  console.log(`  paths checked: ${REQUIRED_PATHS.length}`);
+  console.log(`  schemas checked: ${REQUIRED_SCHEMAS.length}`);
+}
+
+main();