diff --git a/.changeset/strict-brand-domains.md b/.changeset/strict-brand-domains.md
new file mode 100644
index 0000000000..bbd07cd2f4
--- /dev/null
+++ b/.changeset/strict-brand-domains.md
@@ -0,0 +1,5 @@
+---
+"adcontextprotocol": major
+---
+
+Require dotted domains in BrandRef and BrandKey wire schemas, define explicit reserved-domain development exceptions for SDKs, and reserve public registrability plus DNS/SSRF checks for production resolution.
diff --git a/docs/brand-protocol/key-concepts.mdx b/docs/brand-protocol/key-concepts.mdx
index a42e5fa7f4..8ae17b0e69 100644
--- a/docs/brand-protocol/key-concepts.mdx
+++ b/docs/brand-protocol/key-concepts.mdx
@@ -155,6 +155,19 @@ There are three ways to resolve brand identity, each returning the same data str
 
 Regardless of source, the result is a brand identity that can be referenced by any AdCP task via a brand reference (`{ "domain": "...", "brand_id": "..." }`).
 
+`BrandRef.domain` is a lowercase dotted domain, not a local hostname alias. Bare
+names such as `localhost`, `unknown`, and `intranet` are invalid because another
+agent cannot resolve them in the same DNS context. Production resolvers require
+a hostname with a registrable ICANN or private-PSL parent and apply the protocol's DNS and SSRF checks before fetching
+`/.well-known/brand.json`.
+
+For local development and deterministic fixtures, SDKs may explicitly allow
+dotted names under `.localhost`, `.test`, `.example`, or `.invalid` (including
+the reserved `example.com`, `example.net`, and `example.org` names). This must be
+an explicit development option, never inferred from the process environment.
+Bare `localhost` remains invalid, and `.local` is not a development exception
+because it participates in multicast DNS.
+
 ## Use cases
 
 ### Creative generation
diff --git a/scripts/build-protocol-tarball.cjs b/scripts/build-protocol-tarball.cjs
index b1b81754c8..916d2699d8 100644
--- a/scripts/build-protocol-tarball.cjs
+++ b/scripts/build-protocol-tarball.cjs
@@ -168,6 +168,30 @@ function pinPublishedVersion(filePath, publishedVersion) {
   });
 }
 
+function pinSchemaTreeVersion(schemaDir, publishedVersion) {
+  const latestMarker = '/schemas/latest/';
+  const pinnedMarker = `/schemas/${publishedVersion}/`;
+
+  function pinReferences(value) {
+    if (!value || typeof value !== 'object') return false;
+    let changed = false;
+    for (const [key, child] of Object.entries(value)) {
+      if ((key === '$id' || key === '$ref') && typeof child === 'string' && child.includes(latestMarker)) {
+        value[key] = child.replace(latestMarker, pinnedMarker);
+        changed = true;
+      } else if (pinReferences(child)) {
+        changed = true;
+      }
+    }
+    return changed;
+  }
+
+  for (const relativePath of walk(schemaDir)) {
+    if (!relativePath.endsWith('.json')) continue;
+    updateJsonFile(path.join(schemaDir, relativePath), pinReferences);
+  }
+}
+
 function writeBundleReadme(bundleDir, version, isDev) {
   const extractedDir = isDev ? 'adcp-latest' : `adcp-${version}`;
   const quickstart = isDev
@@ -304,6 +328,7 @@ function stageBundle(
   pinGeneratedAt(path.join(schemasDst, 'manifest.json'), metadata.generatedAt);
   if (publishedVersion !== version) {
     pinPublishedVersion(path.join(schemasDst, 'index.json'), publishedVersion);
+    pinSchemaTreeVersion(schemasDst, publishedVersion);
   }
 
   const complianceSource = path.join(DIST_COMPLIANCE, version);
@@ -472,6 +497,7 @@ module.exports = {
   buildTarball,
   pinGeneratedAt,
   pinPublishedVersion,
+  pinSchemaTreeVersion,
   resolveBuildMetadata,
   writeIntegritySidecars
 };
diff --git a/scripts/lint-storyboard-sample-request-schema.cjs b/scripts/lint-storyboard-sample-request-schema.cjs
index 4ae0d6a402..2095a4ce89 100644
--- a/scripts/lint-storyboard-sample-request-schema.cjs
+++ b/scripts/lint-storyboard-sample-request-schema.cjs
@@ -181,6 +181,9 @@ function placeholderFor(schema, depth = 0) {
     if (resolved.pattern === '^sha256:[A-Za-z0-9_-]{43}$') return SHA256_DIGEST_PLACEHOLDER;
     if (resolved.pattern === '^[A-Fa-f0-9]{64}$') return 'a'.repeat(64);
     if (resolved.pattern === '^[A-Z]{3}$') return 'USD';
+    if (resolved.pattern === '^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)+$') {
+      return 'placeholder.example';
+    }
     // Object variant nested inside a oneOf/anyOf at a location where the
     // author's substitution will resolve to that shape at runtime. Synthesize
     // the concrete shape instead of returning a string that fails required.
diff --git a/server/src/brand-manager.ts b/server/src/brand-manager.ts
index e6ba41fb46..23921e9709 100644
--- a/server/src/brand-manager.ts
+++ b/server/src/brand-manager.ts
@@ -13,7 +13,7 @@ import type {
 } from './types';
 import { AAO_UA_VALIDATOR } from './config/user-agents.js';
 import { withSdkSafeTransport } from './utils/sdk-safe-fetch.js';
-import { assertValidBrandDomain } from './services/identifier-normalization.js';
+import { assertRegistrableBrandDomain } from './services/identifier-normalization.js';
 import {
   observeBrandRelationshipDeclaration,
   type BrandRelationshipDeclaration,
@@ -203,15 +203,19 @@ export class BrandManager {
   // Cache for failed lookups (5 minutes, never longer than a resolution miss)
   private failedLookupCache: Cache<BrandValidationResult>;
   private observeRelationshipDeclaration: RelationshipDeclarationObserver;
+  private allowDevelopmentDomains: boolean;
 
   constructor(options: {
     observeRelationshipDeclaration?: RelationshipDeclarationObserver;
+    /** Admit only the protocol's reserved dotted development names. */
+    allowDevelopmentDomains?: boolean;
   } = {}) {
     this.validationCache = new Cache<BrandValidationResult>(BRAND_MANAGER_CACHE_TTL_SECONDS.origin / 60, BRAND_CACHE_MAX_ENTRIES);
     this.resolutionCache = new Cache<ResolvedBrand | null>(BRAND_MANAGER_CACHE_TTL_SECONDS.origin / 60, BRAND_CACHE_MAX_ENTRIES);
     this.failedLookupCache = new Cache<BrandValidationResult>(BRAND_MANAGER_CACHE_TTL_SECONDS.negative / 60, BRAND_FAILED_CACHE_MAX_ENTRIES);
     this.observeRelationshipDeclaration = options.observeRelationshipDeclaration
       ?? observeBrandRelationshipDeclaration;
+    this.allowDevelopmentDomains = options.allowDevelopmentDomains === true;
   }
 
   /**
@@ -273,7 +277,9 @@ export class BrandManager {
       .replace(/^https?:\/\//, '')
       .replace(/\/$/, '');
     try {
-      assertValidBrandDomain(normalized);
+      assertRegistrableBrandDomain(normalized, {
+        allowDevelopmentDomains: this.allowDevelopmentDomains,
+      });
       return normalized;
     } catch {
       return null;
diff --git a/server/src/services/identifier-normalization.ts b/server/src/services/identifier-normalization.ts
index 3d2c337907..9d28e07c1d 100644
--- a/server/src/services/identifier-normalization.ts
+++ b/server/src/services/identifier-normalization.ts
@@ -1,3 +1,5 @@
+import { parse as parseTld } from 'tldts';
+
 /**
  * Identifier normalization for the property catalog.
  *
@@ -22,6 +24,23 @@ export function canonicalizeBrandDomain(raw: string): string {
 }
 
 const BRAND_DOMAIN_RE = /^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)+$/;
+const DEVELOPMENT_DOMAIN_SUFFIXES = ['localhost', 'test', 'example', 'invalid'] as const;
+const DEVELOPMENT_DOMAIN_EXACT_NAMES = new Set(['example.com', 'example.net', 'example.org']);
+const SPECIAL_USE_DOMAIN_SUFFIXES = [
+  'alt', '6tisch.arpa', 'eap.arpa', 'eap-noob.arpa', 'home.arpa',
+  'in-addr.arpa', 'ip6.arpa', 'ipv4only.arpa', 'resolver.arpa', 'service.arpa',
+  'example', 'example.com', 'example.net', 'example.org', 'invalid', 'local',
+  'localhost', 'onion', 'test',
+] as const;
+
+function hasDomainSuffix(domain: string, suffix: string): boolean {
+  return domain === suffix || domain.endsWith(`.${suffix}`);
+}
+
+export function isDevelopmentBrandDomain(domain: string): boolean {
+  return DEVELOPMENT_DOMAIN_EXACT_NAMES.has(domain)
+    || DEVELOPMENT_DOMAIN_SUFFIXES.some((suffix) => domain.endsWith(`.${suffix}`));
+}
 
 /**
  * Throw if the canonicalized value isn't a plausible domain (multi-label,
@@ -30,9 +49,46 @@ const BRAND_DOMAIN_RE = /^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\.[a-z0-9]([a-z0-9-]*[a-
  * profile fields.
  */
 export function assertValidBrandDomain(canonical: string): void {
-  if (!BRAND_DOMAIN_RE.test(canonical) || canonical.length > 253) {
+  if (
+    !BRAND_DOMAIN_RE.test(canonical)
+    || canonical.length > 253
+    || canonical.split('.').some((label) => label.length > 63)
+  ) {
     throw new Error(`"${canonical}" is not a valid brand domain.`);
   }
+
+}
+
+/**
+ * Throw unless a syntactically valid domain has a registrable parent in the
+ * ICANN or private Public Suffix List. Reserved dotted names may be admitted
+ * only by an explicit development-only caller option.
+ */
+export function assertRegistrableBrandDomain(
+  canonical: string,
+  options: { allowDevelopmentDomains?: boolean } = {},
+): void {
+  assertValidBrandDomain(canonical);
+
+  const developmentDomain = isDevelopmentBrandDomain(canonical);
+  if (developmentDomain && options.allowDevelopmentDomains === true) return;
+
+  const parsed = parseTld(canonical, {
+    allowPrivateDomains: true,
+    detectSpecialUse: true,
+    extractHostname: false,
+  });
+  const specialUse = SPECIAL_USE_DOMAIN_SUFFIXES.some((suffix) => hasDomainSuffix(canonical, suffix));
+  if (
+    developmentDomain
+    || specialUse
+    || parsed.isIp
+    || parsed.isSpecialUse
+    || !parsed.domain
+    || (!parsed.isIcann && !parsed.isPrivate)
+  ) {
+    throw new Error(`"${canonical}" is not a registrable production brand domain.`);
+  }
 }
 
 /**
diff --git a/server/tests/unit/brand-manager-cache.test.ts b/server/tests/unit/brand-manager-cache.test.ts
index ed74378bc2..db2e66c121 100644
--- a/server/tests/unit/brand-manager-cache.test.ts
+++ b/server/tests/unit/brand-manager-cache.test.ts
@@ -19,6 +19,7 @@ describe('BrandManager caching', () => {
   let relationshipDeclarations: Map<string, number>;
 
   const createManager = () => new BrandManager({
+    allowDevelopmentDomains: true,
     observeRelationshipDeclaration: async (declaration) => {
       const key = [
         declaration.houseDomain.toLowerCase(),
@@ -50,6 +51,21 @@ describe('BrandManager caching', () => {
   });
 
   describe('validateDomain caching', () => {
+    it.each([
+      '1.2.3.4',
+      'co.uk',
+      'brand.unknown',
+      'brand.localhost',
+      'brand.local',
+      'brand.10.in-addr.arpa',
+      'example.com',
+    ])('rejects non-production domain %s before network access', async (domain) => {
+      const productionManager = new BrandManager();
+      const result = await productionManager.validateDomain(domain);
+      expect(result.valid).toBe(false);
+      expect(mockedSafeFetch).not.toHaveBeenCalled();
+    });
+
     it('caches successful validation results', async () => {
       const mockBrandJson = {
         $schema: 'https://adcontextprotocol.org/schemas/latest/brand.json',
@@ -1299,6 +1315,7 @@ describe('BrandManager caching', () => {
 
     it('fails closed when a missing effective_at cannot be durably observed', async () => {
       manager = new BrandManager({
+        allowDevelopmentDomains: true,
         observeRelationshipDeclaration: async () => {
           throw new Error('database unavailable');
         },
@@ -1317,6 +1334,7 @@ describe('BrandManager caching', () => {
     it('can evaluate explicit effective_at while durable storage is unavailable', async () => {
       const effectiveAt = new Date(Date.now() - 24 * 60 * 60 * 1000).toISOString();
       manager = new BrandManager({
+        allowDevelopmentDomains: true,
         observeRelationshipDeclaration: async () => {
           throw new Error('database unavailable');
         },
diff --git a/server/tests/unit/canonicalize-brand-domain.test.ts b/server/tests/unit/canonicalize-brand-domain.test.ts
index 312fa3e47b..5987509fba 100644
--- a/server/tests/unit/canonicalize-brand-domain.test.ts
+++ b/server/tests/unit/canonicalize-brand-domain.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { canonicalizeBrandDomain, assertValidBrandDomain, assertClaimableBrandDomain } from '../../src/services/identifier-normalization.js';
+import { canonicalizeBrandDomain, assertValidBrandDomain, assertRegistrableBrandDomain, assertClaimableBrandDomain } from '../../src/services/identifier-normalization.js';
 
 describe('canonicalizeBrandDomain', () => {
   it('strips https:// protocol', () => {
@@ -40,7 +40,7 @@ describe('canonicalizeBrandDomain', () => {
   });
 });
 
-describe('assertValidBrandDomain', () => {
+describe('brand domain validation', () => {
   it('accepts a typical apex domain', () => {
     expect(() => assertValidBrandDomain('kyber1.com')).not.toThrow();
   });
@@ -49,6 +49,32 @@ describe('assertValidBrandDomain', () => {
     expect(() => assertValidBrandDomain('app.kyber1.com')).not.toThrow();
   });
 
+  it('rejects public suffixes, unknown suffixes, IP literals, and special-use names', () => {
+    for (const domain of [
+      'co.uk',
+      'brand.unknown',
+      '1.2.3.4',
+      'brand.local',
+      'brand.10.in-addr.arpa',
+      'example.com',
+    ]) {
+      expect(() => assertRegistrableBrandDomain(domain)).toThrow();
+    }
+  });
+
+  it('admits only narrow dotted development names with explicit opt-in', () => {
+    for (const domain of ['brand.localhost', 'brand.test', 'brand.example', 'brand.invalid', 'example.com']) {
+      expect(() => assertRegistrableBrandDomain(domain)).toThrow();
+      expect(() => assertRegistrableBrandDomain(domain, { allowDevelopmentDomains: true })).not.toThrow();
+    }
+    expect(() => assertRegistrableBrandDomain('localhost', { allowDevelopmentDomains: true })).toThrow();
+    expect(() => assertRegistrableBrandDomain('brand.local', { allowDevelopmentDomains: true })).toThrow();
+  });
+
+  it('rejects labels longer than 63 octets', () => {
+    expect(() => assertValidBrandDomain(`${'a'.repeat(64)}.com`)).toThrow();
+  });
+
   it('rejects a single-label hostname', () => {
     expect(() => assertValidBrandDomain('localhost')).toThrow();
   });
@@ -145,7 +171,7 @@ describe('assertClaimableBrandDomain', () => {
   it('does NOT match domains that merely look like a suffix substring', () => {
     // The suffix matcher requires a leading `.`; otherwise `xhubspotusercontent.com`
     // would falsely match `hubspotusercontent.com`.
-    expect(() => assertClaimableBrandDomain('foo.example.com')).not.toThrow();
+    expect(() => assertClaimableBrandDomain('foo.example-corp.com')).not.toThrow();
     expect(() => assertClaimableBrandDomain('myhubspotusercontent.com')).not.toThrow();
   });
 
diff --git a/static/schemas/source/core/brand-key.json b/static/schemas/source/core/brand-key.json
index a57e3bc40f..b8b26df80a 100644
--- a/static/schemas/source/core/brand-key.json
+++ b/static/schemas/source/core/brand-key.json
@@ -7,8 +7,9 @@
   "properties": {
     "domain": {
       "type": "string",
-      "description": "Domain that hosts /.well-known/brand.json or is registered for the brand.",
-      "pattern": "^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)*$"
+      "maxLength": 253,
+      "description": "Lowercase dotted domain that hosts /.well-known/brand.json or is registered for the brand. Single-label names such as localhost and intranet aliases are invalid. This schema checks portable wire syntax only; production resolvers additionally require a registrable domain and reject IP literals, IANA special-use names, and private or reserved resolution targets. SDK development overrides may admit only explicitly configured dotted test names and do not make those names production-conformant.",
+      "pattern": "^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)+$"
     },
     "brand_id": {
       "$ref": "/schemas/core/brand-id.json",
diff --git a/static/schemas/source/core/brand-ref.json b/static/schemas/source/core/brand-ref.json
index e13c3aec71..518283819a 100644
--- a/static/schemas/source/core/brand-ref.json
+++ b/static/schemas/source/core/brand-ref.json
@@ -7,8 +7,9 @@
   "properties": {
     "domain": {
       "type": "string",
-      "description": "Domain where /.well-known/brand.json is hosted, or the brand's operating domain",
-      "pattern": "^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)*$"
+      "maxLength": 253,
+      "description": "Lowercase dotted domain where /.well-known/brand.json is hosted, or the brand's operating domain. Single-label names such as localhost and intranet aliases are invalid. This schema checks portable wire syntax only; production resolvers additionally require a registrable domain and reject IP literals, IANA special-use names, and private or reserved resolution targets. SDK development overrides may admit only explicitly configured dotted test names and do not make those names production-conformant.",
+      "pattern": "^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)+$"
     },
     "brand_id": {
       "$ref": "/schemas/core/brand-id.json",
diff --git a/tests/lint-storyboard-sample-request-schema.test.cjs b/tests/lint-storyboard-sample-request-schema.test.cjs
index 9fa2dcdc85..de2f9e9aee 100644
--- a/tests/lint-storyboard-sample-request-schema.test.cjs
+++ b/tests/lint-storyboard-sample-request-schema.test.cjs
@@ -289,6 +289,13 @@ test('normalizeSubstitutions produces a schema-valid currency placeholder', () =
   }), 'USD');
 });
 
+test('normalizeSubstitutions produces a schema-valid dotted domain placeholder', () => {
+  assert.equal(normalizeSubstitutions('$context.brand_domain', {
+    type: 'string',
+    pattern: '^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)+$',
+  }), 'placeholder.example');
+});
+
 // Object-typed substitution synthesis — the lint change landed in this PR.
 // A substitution that lands at an object location (plain or inside a
 // discriminated oneOf) must produce a shape-valid placeholder or ajv will
diff --git a/tests/schema-validation.test.cjs b/tests/schema-validation.test.cjs
index 3242ebc063..51c348a1c5 100644
--- a/tests/schema-validation.test.cjs
+++ b/tests/schema-validation.test.cjs
@@ -2958,6 +2958,30 @@ async function runTests() {
     return true;
   });
 
+  await test('brand identity references require portable dotted domains', async () => {
+    for (const schemaFile of ['core/brand-ref.json', 'core/brand-key.json']) {
+      const schema = loadSchema(path.join(SCHEMA_BASE_DIR, schemaFile));
+      const testAjv = new Ajv({ allErrors: true, strict: false, loadSchema: loadExternalSchema });
+      addFormats(testAjv);
+      const validate = await testAjv.compileAsync(schema);
+
+      for (const domain of ['brand.example', 'ads.brand.co.uk', 'brand.localhost']) {
+        if (!validate({ domain })) {
+          return `${schemaFile} rejected dotted wire domain ${domain}: ${JSON.stringify(validate.errors)}`;
+        }
+      }
+      for (const domain of ['localhost', 'unknown', 'intranet']) {
+        if (validate({ domain })) {
+          return `${schemaFile} accepted single-label domain ${domain}`;
+        }
+      }
+      if (validate({ domain: `${'a'.repeat(63)}.${'b'.repeat(63)}.${'c'.repeat(63)}.${'d'.repeat(62)}` })) {
+        return `${schemaFile} accepted a domain longer than 253 characters`;
+      }
+    }
+    return true;
+  });
+
   // Test 13: Validate schema examples against their schemas
   await test('Schema examples validate against their own schemas', async () => {
     // Skip schemas that require format-aware validation (creative manifests need format context)
diff --git a/tests/sign-protocol-tarball.test.cjs b/tests/sign-protocol-tarball.test.cjs
index 117dea8ff4..0c7fd263a7 100644
--- a/tests/sign-protocol-tarball.test.cjs
+++ b/tests/sign-protocol-tarball.test.cjs
@@ -12,6 +12,7 @@ const {
   buildTarball,
   pinGeneratedAt,
   pinPublishedVersion,
+  pinSchemaTreeVersion,
   resolveBuildMetadata,
   writeIntegritySidecars,
 } = require('../scripts/build-protocol-tarball.cjs');
@@ -257,4 +258,29 @@ describe('build-protocol-tarball.cjs', () => {
       fs.rmSync(tmp, { recursive: true, force: true });
     }
   });
+
+  it('pins schema ids and references in release-compatible PR bundles', () => {
+    const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'adcp-protocol-schema-tree-'));
+    try {
+      fs.mkdirSync(path.join(tmp, 'core'), { recursive: true });
+      const schemaPath = path.join(tmp, 'core', 'manifest.json');
+      fs.writeFileSync(schemaPath, JSON.stringify({
+        $id: 'https://adcontextprotocol.org/schemas/latest/core/manifest.json',
+        properties: {
+          entry: { $ref: '/schemas/latest/core/entry.json' },
+        },
+      }));
+
+      pinSchemaTreeVersion(tmp, '3.2.0-beta.9');
+
+      assert.deepEqual(JSON.parse(fs.readFileSync(schemaPath, 'utf8')), {
+        $id: 'https://adcontextprotocol.org/schemas/3.2.0-beta.9/core/manifest.json',
+        properties: {
+          entry: { $ref: '/schemas/3.2.0-beta.9/core/entry.json' },
+        },
+      });
+    } finally {
+      fs.rmSync(tmp, { recursive: true, force: true });
+    }
+  });
 });