diff --git a/packages/spacecat-shared-data-access/src/models/plg-onboarding/plg-onboarding.model.js b/packages/spacecat-shared-data-access/src/models/plg-onboarding/plg-onboarding.model.js
index 25c834619..4523fc1ee 100644
--- a/packages/spacecat-shared-data-access/src/models/plg-onboarding/plg-onboarding.model.js
+++ b/packages/spacecat-shared-data-access/src/models/plg-onboarding/plg-onboarding.model.js
@@ -24,7 +24,90 @@ class PlgOnboarding extends BaseModel {
 
   static IMS_ORG_ID_PATTERN = /^[a-z0-9]{24}@AdobeOrg$/i;
 
-  static DOMAIN_PATTERN = /^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)*$/;
+  static MAX_HOSTNAME_LENGTH = 253; // RFC 1035 DNS name limit
+
+  // Practical cap, chosen for storage and sort-key index depth rather than for any
+  // specific browser/URL-bar limit (the domain field is a stored identifier, not a URL).
+  static MAX_DOMAIN_LENGTH = 2048;
+
+  // **WARNING for external consumers: do NOT use DOMAIN_PATTERN directly.**
+  // This regex is incomplete on its own — it has no length cap, no control-character
+  // rejection, no all-numeric-hostname check, no trailing-dot/consecutive-dot path
+  // rejection, and no typeof guard. Always call `PlgOnboarding.isValidDomain(value)`
+  // which composes this regex with the rest of the validator. The regex is exported
+  // only for legacy callers and may become module-private in a future major release.
+  //
+  // Matches lowercase hostnames (at least one dot required) and an optional subpath
+  //   (e.g. nba.com, nba.com/kings, nba.com/us/kings).
+  // The final label (TLD) must be alphabetic (>= 2 chars) or punycode (xn--*). This
+  //   structurally rejects every IP-literal form: dotted-quad (127.0.0.1), short-form
+  //   (127.1), decimal (2130706433), hex (0x7f.0.0.1, 0xa9.254.169.254 → AWS IMDS),
+  //   and octal (0177.0.0.1) — and also blocks foo.1-style typos. WHATWG URL would
+  //   otherwise canonicalize hex/decimal IPs to their dotted-quad form, bypassing
+  //   denylist-based SSRF gates downstream.
+  // Rejects: uppercase letters (use normalizeDomain() first), schemes (https://),
+  //   ports (:8080), single-label hostnames (localhost, metadata), query strings,
+  //   fragments, empty/trailing path segments, and any path segment starting with
+  //   a dot (blocks ./, ../, .hidden, ..foo, etc.).
+  // Path-qualified domains (nba.com/kings) are distinct sort-key values from the bare
+  //   hostname; callers must call normalizeDomain() before findByImsOrgIdAndDomain.
+  // Labels must not start or end with a hyphen (RFC 1035).
+  // Raw Unicode / IDN must be punycode-encoded before validation (xn-- form is accepted).
+  // Percent-encoded path characters (%20 etc.) are not accepted; decode before validation.
+  // Underscore is allowed in path segments but not in hostname labels.
+  static DOMAIN_PATTERN = /^[a-z0-9](?:[a-z0-9-]*[a-z0-9])?(?:\.[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)*\.(?:[a-z]{2,}|xn--[a-z0-9-]+)(\/(?!\.)[a-z0-9._~-]+)*$/;
+
+  // Returns the canonical form of a domain value: lowercased.
+  // Note: non-string inputs (null/undefined/number/object) are returned unchanged.
+  // Callers MUST also run `isValidDomain(value)` before using the result — calling
+  // `normalizeDomain` alone does not guarantee the value is a string or safe to
+  // pass to `findByImsOrgIdAndDomain` (which would otherwise treat a non-string
+  // sort key as something it isn't).
+  static normalizeDomain(value) {
+    return typeof value === 'string' ? value.toLowerCase() : value;
+  }
+
+  // Complete domain validator used by the schema and intended for external consumers.
+  // Layers a typeof guard, case-canonical check, control-character rejection,
+  // all-numeric-hostname rejection (defense-in-depth; DOMAIN_PATTERN's alphabetic-TLD
+  // requirement already rejects dotted-quad, short-form, decimal, hex, and octal IPs),
+  // trailing-dot path-segment rejection, DOMAIN_PATTERN test, and length caps.
+  // Note: DOMAIN_PATTERN alone is not sufficient — always prefer this method.
+  // Lowercase-only (host AND path) is intentional canonicalization, not a bug. The
+  // domain field is part of the dedup sort key on findByImsOrgIdAndDomain; allowing
+  // mixed-case paths would let `nba.com/Kings` and `nba.com/kings` create distinct
+  // onboarding rows for the same site. Callers should call normalizeDomain() first.
+  // This is a syntactic / data-integrity validator, not an SSRF gate. Callers that
+  // make outbound fetches must layer their own private-IP and DNS-resolution checks.
+  static isValidDomain(value) {
+    if (typeof value !== 'string' || value !== value.toLowerCase()) {
+      return false;
+    }
+    // Length caps run BEFORE the regex test so a multi-MB pathological input is
+    // rejected in O(1) rather than driving a multi-MB regex scan. The regex itself
+    // is linear (no overlapping quantifiers) but external consumers may not bound
+    // input size upstream.
+    if (value.length > PlgOnboarding.MAX_DOMAIN_LENGTH) {
+      return false;
+    }
+    if (/[^\x21-\x7e]/.test(value)) {
+      return false;
+    }
+    const [hostname, ...pathParts] = value.split('/');
+    if (hostname.length > PlgOnboarding.MAX_HOSTNAME_LENGTH) {
+      return false;
+    }
+    if (/^[\d.]+$/.test(hostname)) {
+      return false;
+    }
+    // Reject path segments that are purely dots, end with a dot, or contain
+    // consecutive dots (foo., foo.., foo../bar, v1..0). DOMAIN_PATTERN's
+    // negative lookahead only blocks segments STARTING with a dot.
+    if (pathParts.some((seg) => /\.$/.test(seg) || seg.includes('..'))) {
+      return false;
+    }
+    return PlgOnboarding.DOMAIN_PATTERN.test(value);
+  }
 
   static STATUSES = {
     PRE_ONBOARDING: 'PRE_ONBOARDING',
diff --git a/packages/spacecat-shared-data-access/src/models/plg-onboarding/plg-onboarding.schema.js b/packages/spacecat-shared-data-access/src/models/plg-onboarding/plg-onboarding.schema.js
index 5233a4f6b..ec327015d 100644
--- a/packages/spacecat-shared-data-access/src/models/plg-onboarding/plg-onboarding.schema.js
+++ b/packages/spacecat-shared-data-access/src/models/plg-onboarding/plg-onboarding.schema.js
@@ -28,7 +28,7 @@ const schema = new SchemaBuilder(PlgOnboarding, PlgOnboardingCollection)
     type: 'string',
     required: true,
     readOnly: true,
-    validate: (value) => PlgOnboarding.DOMAIN_PATTERN.test(value) && value.length <= 253,
+    validate: (value) => PlgOnboarding.isValidDomain(value),
   })
   .addAttribute('baseURL', {
     type: 'string',
diff --git a/packages/spacecat-shared-data-access/test/unit/models/plg-onboarding/plg-onboarding.model.test.js b/packages/spacecat-shared-data-access/test/unit/models/plg-onboarding/plg-onboarding.model.test.js
index 162e60248..537ec278f 100644
--- a/packages/spacecat-shared-data-access/test/unit/models/plg-onboarding/plg-onboarding.model.test.js
+++ b/packages/spacecat-shared-data-access/test/unit/models/plg-onboarding/plg-onboarding.model.test.js
@@ -79,6 +79,226 @@ describe('PlgOnboardingModel', () => {
     });
   });
 
+  describe('DOMAIN_PATTERN', () => {
+    const { DOMAIN_PATTERN } = PlgOnboarding;
+
+    describe('valid values', () => {
+      [
+        'nba.com',
+        'www.nba.com',
+        'sub.domain.example.com',
+        'nba.com/kings',
+        'nba.com/us/kings',
+        'example.com/path/with-hyphens',
+        'example.com/path.with.dots',
+        'example.io/a/b/c',
+        'example.com/en-us',
+        'example.com/case_studies',
+        'xn--nba-6na.com',
+        // Hostnames that begin with a dotted-quad-shaped prefix but end in an
+        // alphabetic TLD remain valid — IP literals are blocked by the TLD
+        // requirement (final label must be [a-z]{2,} or xn--*), not by a
+        // lookahead. Covers nip.io-style wildcard DNS.
+        '1.2.3.4.example.com',
+        '192.168.1.1.nip.io',
+      ].forEach((value) => {
+        it(`accepts "${value}"`, () => {
+          expect(DOMAIN_PATTERN.test(value)).to.be.true;
+        });
+      });
+    });
+
+    describe('invalid values', () => {
+      [
+        ['empty string', ''],
+        ['scheme prefix', 'https://nba.com'],
+        ['scheme prefix http', 'http://nba.com'],
+        ['IPv4 address', '127.0.0.1'],
+        ['IPv4 address 8.8.8.8', '8.8.8.8'],
+        ['IPv4 with path', '127.0.0.1/path'],
+        ['query string', 'nba.com?foo=bar'],
+        ['fragment', 'nba.com#section'],
+        ['path with query string', 'nba.com/kings?q=1'],
+        ['path with fragment', 'nba.com/kings#top'],
+        ['trailing hyphen in label', 'nba-.com'],
+        ['trailing hyphen in subdomain', 'foo-.nba.com'],
+        ['trailing slash', 'nba.com/'],
+        ['trailing slash after path', 'nba.com/kings/'],
+        ['double slash', 'nba.com//kings'],
+        ['port number', 'nba.com:8080'],
+        ['path traversal dot-dot', 'nba.com/../etc'],
+        ['path traversal dot', 'nba.com/./x'],
+        ['path traversal dot-dot at end', 'nba.com/..'],
+        ['path traversal dot at end', 'nba.com/.'],
+        ['leading dot in path segment', 'nba.com/.hidden'],
+        ['leading double-dot prefix in segment', 'nba.com/..foo'],
+        ['trailing dot fqdn', 'nba.com.'],
+        ['single-label hostname', 'localhost'],
+        ['single-label intranet hostname', 'intranet'],
+        ['uppercase hostname', 'NBA.COM'],
+        ['uppercase path segment', 'nba.com/Kings'],
+        ['uppercase locale path', 'example.com/en-US'],
+        ['IPv6 bracketed', '[::1]'],
+        ['IPv6 unbracketed', '2001:db8::1'],
+        ['percent-encoded path', 'nba.com/path%20with%20space'],
+        // IP-literal forms rejected via the alphabetic/punycode TLD requirement.
+        ['hex IPv4', '0x7f.0.0.1'],
+        ['hex IPv4 (IMDS)', '0xa9.254.169.254'],
+        ['octal IPv4', '0177.0.0.1'],
+        ['short-form IPv4', '127.1'],
+        ['numeric TLD', 'foo.1'],
+      ].forEach(([label, value]) => {
+        it(`rejects ${label}: "${value}"`, () => {
+          expect(DOMAIN_PATTERN.test(value)).to.be.false;
+        });
+      });
+    });
+  });
+
+  describe('isValidDomain', () => {
+    describe('valid values', () => {
+      [
+        'nba.com',
+        'www.nba.com',
+        'nba.com/kings',
+        'nba.com/us/kings',
+        'example.com/en-us',
+        'example.com/case_studies',
+        'xn--nba-6na.com',
+        // Hostnames that start with a dotted-quad but continue with non-IP labels:
+        // IP literals are rejected via the alphabetic/punycode TLD requirement,
+        // not via a hostname-prefix lookahead, so these legitimate hosts pass.
+        '1.2.3.4.example.com',
+        '192.168.1.1.nip.io',
+      ].forEach((value) => {
+        it(`accepts "${value}"`, () => {
+          expect(PlgOnboarding.isValidDomain(value)).to.be.true;
+        });
+      });
+    });
+
+    describe('invalid values', () => {
+      [
+        ['empty string', ''],
+        ['scheme prefix', 'https://nba.com'],
+        ['IPv4 address', '127.0.0.1'],
+        ['short-form IPv4', '127.1'],
+        ['decimal IPv4', '2130706433'],
+        ['uppercase hostname', 'NBA.COM'],
+        ['uppercase path segment', 'nba.com/Kings'],
+        ['null byte in domain', 'nba.com\x00/evil'],
+        ['control character in path', 'nba.com/ki\x01ngs'],
+        ['trailing dot path segment', 'nba.com/foo.'],
+        ['trailing dot fqdn', 'nba.com.'],
+        ['consecutive dots mid path segment', 'nba.com/v1..0'],
+        ['consecutive dots mid path segment 2', 'nba.com/foo..bar'],
+        // Hex-encoded IPv4 literals (WHATWG URL canonicalizes these to dotted-quad,
+        // bypassing denylist-based SSRF gates that match raw strings).
+        ['hex IPv4', '0x7f.0.0.1'],
+        ['hex IPv4 (IMDS)', '0xa9.254.169.254'],
+        ['hex IPv4 all hex', '0xa9.0xfe.0xa9.0xfe'],
+        ['octal IPv4', '0177.0.0.1'],
+        ['numeric TLD', 'foo.1'],
+      ].forEach(([label, value]) => {
+        it(`rejects ${label}`, () => {
+          expect(PlgOnboarding.isValidDomain(value)).to.be.false;
+        });
+      });
+    });
+
+    describe('non-string inputs', () => {
+      [
+        ['null', null],
+        ['undefined', undefined],
+        ['number', 123],
+        ['boolean', true],
+        ['object', { domain: 'nba.com' }],
+        ['array', ['nba.com']],
+      ].forEach(([label, value]) => {
+        it(`rejects ${label}`, () => {
+          expect(PlgOnboarding.isValidDomain(value)).to.be.false;
+        });
+      });
+    });
+
+    describe('length boundaries', () => {
+      it('accepts a hostname of exactly 253 chars', () => {
+        const hostname = `${'a'.repeat(249)}.com`;
+        expect(hostname.length).to.equal(253);
+        expect(PlgOnboarding.isValidDomain(hostname)).to.be.true;
+      });
+
+      it('rejects a hostname exceeding 253 chars', () => {
+        const hostname = `${'a'.repeat(250)}.com`;
+        expect(hostname.length).to.equal(254);
+        expect(PlgOnboarding.isValidDomain(hostname)).to.be.false;
+      });
+
+      it('accepts a domain of exactly 2048 chars', () => {
+        const value = `nba.com/${'a'.repeat(2040)}`;
+        expect(value.length).to.equal(2048);
+        expect(PlgOnboarding.isValidDomain(value)).to.be.true;
+      });
+
+      it('rejects a domain exceeding 2048 chars', () => {
+        const value = `nba.com/${'a'.repeat(2041)}`;
+        expect(value.length).to.equal(2049);
+        expect(PlgOnboarding.isValidDomain(value)).to.be.false;
+      });
+    });
+
+    describe('regression: DOMAIN_PATTERN alone is insufficient', () => {
+      // Pinning tests: these inputs pass the bare regex but are correctly rejected
+      // by the full validator. They exist to prevent regressions if a future caller
+      // is tempted to import DOMAIN_PATTERN directly instead of isValidDomain.
+      it('DOMAIN_PATTERN accepts trailing-dot path segment but isValidDomain rejects it', () => {
+        expect(PlgOnboarding.DOMAIN_PATTERN.test('nba.com/foo.')).to.be.true;
+        expect(PlgOnboarding.isValidDomain('nba.com/foo.')).to.be.false;
+      });
+
+      it('DOMAIN_PATTERN accepts consecutive-dot path segment but isValidDomain rejects it', () => {
+        expect(PlgOnboarding.DOMAIN_PATTERN.test('nba.com/v1..0')).to.be.true;
+        expect(PlgOnboarding.isValidDomain('nba.com/v1..0')).to.be.false;
+      });
+
+      it('DOMAIN_PATTERN has no length cap but isValidDomain enforces 2048', () => {
+        const tooLong = `nba.com/${'a'.repeat(2041)}`;
+        expect(tooLong.length).to.equal(2049);
+        expect(PlgOnboarding.DOMAIN_PATTERN.test(tooLong)).to.be.true;
+        expect(PlgOnboarding.isValidDomain(tooLong)).to.be.false;
+      });
+    });
+
+    describe('SSRF defense: IP-literal hostnames rejected via TLD requirement', () => {
+      // These would canonicalize to private/loopback IPs via WHATWG URL parsing
+      // (new URL('https://0xa9.254.169.254').hostname → '169.254.169.254').
+      // The alphabetic/punycode TLD requirement in DOMAIN_PATTERN rejects them at
+      // the structural level so downstream raw-string denylists cannot be bypassed.
+      [
+        ['hex IPv4 loopback', '0x7f.0.0.1', '127.0.0.1'],
+        ['hex IPv4 IMDS', '0xa9.254.169.254', '169.254.169.254'],
+        ['hex IPv4 all hex', '0xa9.0xfe.0xa9.0xfe', '169.254.169.254'],
+        ['hex IPv4 RFC1918', '0xa.0.0.1', '10.0.0.1'],
+        ['octal IPv4', '0177.0.0.1', '127.0.0.1'],
+      ].forEach(([label, input]) => {
+        it(`isValidDomain rejects ${label} (${input})`, () => {
+          expect(PlgOnboarding.isValidDomain(input)).to.be.false;
+        });
+      });
+    });
+  });
+
+  describe('normalizeDomain', () => {
+    it('lowercases a string value', () => {
+      expect(PlgOnboarding.normalizeDomain('NBA.COM/Kings')).to.equal('nba.com/kings');
+    });
+
+    it('returns non-string values unchanged', () => {
+      expect(PlgOnboarding.normalizeDomain(null)).to.be.null;
+      expect(PlgOnboarding.normalizeDomain(undefined)).to.be.undefined;
+    });
+  });
+
   describe('REVIEW_DECISIONS', () => {
     it('defines all expected review decisions', () => {
       expect(PlgOnboarding.REVIEW_DECISIONS).to.deep.equal({
diff --git a/packages/spacecat-shared-data-access/test/unit/models/plg-onboarding/plg-onboarding.schema.test.js b/packages/spacecat-shared-data-access/test/unit/models/plg-onboarding/plg-onboarding.schema.test.js
index ab5cc7f40..0918ea738 100644
--- a/packages/spacecat-shared-data-access/test/unit/models/plg-onboarding/plg-onboarding.schema.test.js
+++ b/packages/spacecat-shared-data-access/test/unit/models/plg-onboarding/plg-onboarding.schema.test.js
@@ -14,6 +14,128 @@ import { expect } from 'chai';
 import plgOnboardingSchema from '../../../../src/models/plg-onboarding/plg-onboarding.schema.js';
 
 describe('PlgOnboarding Schema', () => {
+  describe('domain attribute', () => {
+    let domainAttr;
+
+    before(() => {
+      const attributes = plgOnboardingSchema.getAttributes();
+      domainAttr = attributes.domain;
+    });
+
+    it('is a required read-only string', () => {
+      expect(domainAttr.type).to.equal('string');
+      expect(domainAttr.required).to.be.true;
+      expect(domainAttr.readOnly).to.be.true;
+    });
+
+    it('has a validate function', () => {
+      expect(domainAttr.validate).to.be.a('function');
+    });
+
+    describe('valid values', () => {
+      [
+        'nba.com',
+        'www.nba.com',
+        'nba.com/kings',
+        'nba.com/us/kings',
+        'example.com/path-with-hyphens',
+        'example.com/en-us',
+        'example.com/case_studies',
+        'xn--nba-6na.com',
+        'example.com/foo_bar',
+        'example.com/us/foo_bar',
+        '1.2.3.4.example.com',
+        '192.168.1.1.nip.io',
+      ].forEach((value) => {
+        it(`accepts "${value}"`, () => {
+          expect(domainAttr.validate(value)).to.be.true;
+        });
+      });
+    });
+
+    describe('invalid values', () => {
+      [
+        ['empty string', ''],
+        ['scheme prefix', 'https://nba.com'],
+        ['IPv4 address', '127.0.0.1'],
+        ['short-form IPv4', '127.1'],
+        ['decimal IPv4', '2130706433'],
+        ['query string', 'nba.com?q=1'],
+        ['fragment', 'nba.com#top'],
+        ['hostname over 253 chars', `${'a'.repeat(250)}.com`],
+        ['trailing hyphen in label', 'nba-.com'],
+        ['trailing slash', 'nba.com/kings/'],
+        ['path traversal', 'nba.com/../etc'],
+        ['leading dot in path segment', 'nba.com/.hidden'],
+        ['leading double-dot prefix in segment', 'nba.com/..foo'],
+        ['trailing dot fqdn', 'nba.com.'],
+        ['single-label hostname', 'localhost'],
+        ['uppercase hostname', 'NBA.COM'],
+        ['uppercase path segment', 'nba.com/Kings'],
+        ['uppercase locale path', 'example.com/en-US'],
+        ['underscore in hostname label', 'foo_bar.com'],
+        ['underscore in subdomain label', 'foo_bar.example.com'],
+        ['trailing dot in path segment', 'nba.com/foo.'],
+        ['trailing double-dot in path segment', 'nba.com/foo..'],
+        ['dot-dot mid-path segment', 'nba.com/foo../bar'],
+        ['consecutive dots mid path segment', 'nba.com/v1..0'],
+        ['consecutive dots in middle of segment', 'nba.com/foo..bar'],
+        ['null byte in domain', 'nba.com\x00/evil'],
+        ['control character in path', 'nba.com/ki\x01ngs'],
+        ['hex IPv4 loopback', '0x7f.0.0.1'],
+        ['hex IPv4 IMDS', '0xa9.254.169.254'],
+        ['octal IPv4', '0177.0.0.1'],
+        ['numeric TLD', 'foo.1'],
+      ].forEach(([label, value]) => {
+        it(`rejects ${label}`, () => {
+          expect(domainAttr.validate(value)).to.be.false;
+        });
+      });
+    });
+
+    it('allows a plain hostname of exactly 253 chars', () => {
+      const hostname = `${'a'.repeat(249)}.com`;
+      expect(hostname.length).to.equal(253);
+      expect(domainAttr.validate(hostname)).to.be.true;
+    });
+
+    it('rejects a plain hostname exceeding 253 chars', () => {
+      const hostname = `${'a'.repeat(250)}.com`;
+      expect(hostname.length).to.equal(254);
+      expect(domainAttr.validate(hostname)).to.be.false;
+    });
+
+    it('allows a subpath domain whose hostname is exactly 253 chars', () => {
+      const hostname = `${'a'.repeat(249)}.com`;
+      expect(hostname.length).to.equal(253);
+      expect(domainAttr.validate(`${hostname}/path`)).to.be.true;
+    });
+
+    it('rejects when only the hostname exceeds 253 chars (path does not inflate count)', () => {
+      const hostname = `${'a'.repeat(250)}.com`;
+      expect(hostname.length).to.equal(254);
+      expect(domainAttr.validate(`${hostname}/path`)).to.be.false;
+    });
+
+    it('accepts a domain of exactly 2048 chars', () => {
+      const longPath = `nba.com/${'a'.repeat(2040)}`;
+      expect(longPath.length).to.equal(2048);
+      expect(domainAttr.validate(longPath)).to.be.true;
+    });
+
+    it('rejects a domain of exactly 2049 chars', () => {
+      const longPath = `nba.com/${'a'.repeat(2041)}`;
+      expect(longPath.length).to.equal(2049);
+      expect(domainAttr.validate(longPath)).to.be.false;
+    });
+
+    it('rejects when total domain length exceeds 2048 chars', () => {
+      const longPath = `nba.com/${'a'.repeat(2042)}`;
+      expect(longPath.length).to.be.above(2048);
+      expect(domainAttr.validate(longPath)).to.be.false;
+    });
+  });
+
   describe('reviews attribute', () => {
     let reviewsAttr;