diff --git a/packages/server/src/utils/inviteService.test.ts b/packages/server/src/utils/inviteService.test.ts
index 5f94b4cf..05fa529d 100644
--- a/packages/server/src/utils/inviteService.test.ts
+++ b/packages/server/src/utils/inviteService.test.ts
@@ -1,5 +1,52 @@
-import { describe, it, expect } from 'vitest';
-import { inviteStatus, generateInviteToken } from './inviteService.js';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import Database from 'better-sqlite3';
+import { drizzle } from 'drizzle-orm/better-sqlite3';
+import * as schema from '../db/schema.js';
+import { setWorkerId } from './snowflake.js';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+setWorkerId(1);
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+type TestDb = ReturnType<typeof drizzle<typeof schema>>;
+let sqlite: Database.Database;
+let testDb: TestDb;
+
+vi.mock('../db/index.js', () => ({
+  getDb: () => testDb,
+  getRawDb: () => sqlite,
+  schema,
+}));
+
+import { inviteStatus, generateInviteToken, createInvite, getInviteByToken } from './inviteService.js';
+
+function applyMigrations(db: Database.Database): void {
+  const migrationsDir = path.resolve(__dirname, '../../drizzle');
+  const files = fs.readdirSync(migrationsDir).filter(f => f.endsWith('.sql')).sort();
+  for (const f of files) {
+    const sqlText = fs.readFileSync(path.join(migrationsDir, f), 'utf8');
+    const statements = sqlText.split(/-->\s*statement-breakpoint/);
+    for (const stmt of statements) {
+      const clean = stmt.trim();
+      if (clean) db.exec(clean);
+    }
+  }
+}
+
+function seedAdmin(): string {
+  const adminId = 'admin-user-1';
+  testDb.insert(schema.users).values({
+    id: adminId,
+    username: 'admin',
+    passwordHash: 'x',
+    isAdmin: 1,
+    createdAt: Date.now(),
+  }).run();
+  return adminId;
+}
 
 describe('inviteStatus', () => {
   const base = { revokedAt: null, expiresAt: null, maxUses: null, usedCount: 0 };
@@ -54,3 +101,74 @@ describe('generateInviteToken', () => {
     expect(a).not.toBe(b);
   });
 });
+
+describe('createInvite', () => {
+  beforeEach(() => {
+    sqlite = new Database(':memory:');
+    sqlite.pragma('foreign_keys = ON');
+    applyMigrations(sqlite);
+    testDb = drizzle(sqlite, { schema });
+  });
+
+  it('creates an invite with required fields', () => {
+    const adminId = seedAdmin();
+    const invite = createInvite({ name: 'Friends batch 1', maxUses: 10, expiresAt: Date.now() + 86_400_000 }, adminId);
+    expect(invite.name).toBe('Friends batch 1');
+    expect(invite.maxUses).toBe(10);
+    expect(invite.usedCount).toBe(0);
+    expect(invite.revokedAt).toBeNull();
+    expect(invite.token).toMatch(/^[A-Za-z0-9_-]{22}$/);
+    expect(invite.status).toBe('active');
+    expect(invite.createdBy).toBe(adminId);
+    expect(invite.createdByUsername).toBe('admin');
+  });
+
+  it('accepts null maxUses (unlimited)', () => {
+    const adminId = seedAdmin();
+    const invite = createInvite({ name: 'unlimited', maxUses: null, expiresAt: null }, adminId);
+    expect(invite.maxUses).toBeNull();
+    expect(invite.expiresAt).toBeNull();
+    expect(invite.status).toBe('active');
+  });
+
+  it('rejects empty name', () => {
+    const adminId = seedAdmin();
+    expect(() => createInvite({ name: '', maxUses: null, expiresAt: null }, adminId)).toThrow();
+  });
+
+  it('rejects name longer than 64 chars', () => {
+    const adminId = seedAdmin();
+    expect(() => createInvite({ name: 'x'.repeat(65), maxUses: null, expiresAt: null }, adminId)).toThrow();
+  });
+
+  it('rejects non-positive maxUses', () => {
+    const adminId = seedAdmin();
+    expect(() => createInvite({ name: 'a', maxUses: 0, expiresAt: null }, adminId)).toThrow();
+    expect(() => createInvite({ name: 'a', maxUses: -1, expiresAt: null }, adminId)).toThrow();
+  });
+
+  it('rejects past expiresAt', () => {
+    const adminId = seedAdmin();
+    expect(() => createInvite({ name: 'a', maxUses: null, expiresAt: Date.now() - 1000 }, adminId)).toThrow();
+  });
+});
+
+describe('getInviteByToken', () => {
+  beforeEach(() => {
+    sqlite = new Database(':memory:');
+    sqlite.pragma('foreign_keys = ON');
+    applyMigrations(sqlite);
+    testDb = drizzle(sqlite, { schema });
+  });
+
+  it('returns the invite when token matches', () => {
+    const adminId = seedAdmin();
+    const created = createInvite({ name: 'a', maxUses: null, expiresAt: null }, adminId);
+    const found = getInviteByToken(created.token);
+    expect(found?.id).toBe(created.id);
+  });
+
+  it('returns null when token not found', () => {
+    expect(getInviteByToken('nonexistent_token_aaaaaa')).toBeNull();
+  });
+});
diff --git a/packages/server/src/utils/inviteService.ts b/packages/server/src/utils/inviteService.ts
index f1de9245..97efde7b 100644
--- a/packages/server/src/utils/inviteService.ts
+++ b/packages/server/src/utils/inviteService.ts
@@ -1,4 +1,9 @@
 import crypto from 'node:crypto';
+import { eq } from 'drizzle-orm';
+import { getDb, schema } from '../db/index.js';
+import { generateSnowflake } from './snowflake.js';
+import { config } from '../config.js';
+import type { InviteLinkSummary, CreateInviteRequest } from '@backspace/shared';
 
 /**
  * Derived status of an invite link. Mirrors the `InviteStatus` union exported
@@ -39,3 +44,156 @@ export function inviteStatus(row: InviteStatusInput): InviteStatus {
 export function generateInviteToken(): string {
   return crypto.randomBytes(16).toString('base64url');
 }
+
+/**
+ * Thrown by invite-service mutations when caller-supplied input violates a
+ * field rule (length, sign, ordering, etc.). Caller (HTTP route) maps this to
+ * a 400 Bad Request with the message as `error`.
+ */
+export class InviteValidationError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = 'InviteValidationError';
+  }
+}
+
+/**
+ * Build the public-facing invite URL embedded in API responses. Production
+ * deployments always set `DOMAIN`; the localhost fallback is only used in
+ * local dev (where `config.host` is typically `0.0.0.0` and unusable as a
+ * URL host). Per spec §1.2 + §5.4 the server owns URL construction so
+ * clients never have to assemble it.
+ */
+function buildInviteUrl(token: string): string {
+  if (config.domain) return `https://${config.domain}/register?invite=${token}`;
+  return `http://localhost:${config.port}/register?invite=${token}`;
+}
+
+/**
+ * Validate the invite name (1–64 chars after trim). Trimming is part of
+ * normalization so `"  foo  "` is stored as `"foo"`.
+ */
+function validateName(name: string): string {
+  const trimmed = (name ?? '').trim();
+  if (trimmed.length < 1 || trimmed.length > 64) {
+    throw new InviteValidationError('Name must be 1-64 characters');
+  }
+  return trimmed;
+}
+
+/**
+ * Validate `maxUses`: `null` means unlimited; otherwise a positive integer.
+ * Zero is rejected because an invite that can never be used is meaningless
+ * (use revoke for that).
+ */
+function validateMaxUses(maxUses: number | null): number | null {
+  if (maxUses === null) return null;
+  if (!Number.isInteger(maxUses) || maxUses < 1) {
+    throw new InviteValidationError('maxUses must be a positive integer or null');
+  }
+  return maxUses;
+}
+
+/**
+ * Validate `expiresAt` (epoch ms). On create, must be in the future; on
+ * patch/reinstate, `allowPast` lets admins keep an unchanged past value or
+ * deliberately set a past expiry to soft-shut. `Date.now()` exactly is not
+ * "in the future" and is rejected when `allowPast` is false.
+ */
+function validateExpiresAt(expiresAt: number | null, allowPast: boolean): number | null {
+  if (expiresAt === null) return null;
+  if (!Number.isInteger(expiresAt)) {
+    throw new InviteValidationError('expiresAt must be an integer epoch ms or null');
+  }
+  if (!allowPast && expiresAt <= Date.now()) {
+    throw new InviteValidationError('expiresAt must be in the future');
+  }
+  return expiresAt;
+}
+
+/**
+ * Project an `invite_links` row plus the resolved creator-username into the
+ * shared `InviteLinkSummary` shape. Centralized so list/create/patch/reinstate
+ * all return identically-shaped rows. Status is derived (never stored) per
+ * spec §2.1.
+ */
+function rowToSummary(
+  row: typeof schema.inviteLinks.$inferSelect,
+  createdByUsername: string | null,
+): InviteLinkSummary {
+  return {
+    id: row.id,
+    token: row.token,
+    name: row.name,
+    status: inviteStatus(row),
+    maxUses: row.maxUses,
+    usedCount: row.usedCount,
+    expiresAt: row.expiresAt,
+    revokedAt: row.revokedAt,
+    createdBy: row.createdBy,
+    createdByUsername,
+    createdAt: row.createdAt,
+    url: buildInviteUrl(row.token),
+  };
+}
+
+/**
+ * Resolve the username to display for an invite's creator. Returns the live
+ * username, `'Deleted User'` for tombstoned accounts (spec §3.1, §4.1), or
+ * `null` if the FK is unresolvable (defensive — should not happen in practice).
+ */
+function resolveCreatorUsername(creatorId: string): string | null {
+  const db = getDb();
+  const u = db.select({ username: schema.users.username, isDeleted: schema.users.isDeleted })
+    .from(schema.users)
+    .where(eq(schema.users.id, creatorId))
+    .get();
+  if (!u) return null;
+  if (u.isDeleted === 1) return 'Deleted User';
+  return u.username;
+}
+
+/**
+ * Create a new invite link. Validates input, generates id + token, inserts the
+ * row, and returns the projected summary. Throws `InviteValidationError` on
+ * bad input (caller maps to 400).
+ */
+export function createInvite(req: CreateInviteRequest, creatorId: string): InviteLinkSummary {
+  const name = validateName(req.name);
+  const maxUses = validateMaxUses(req.maxUses);
+  const expiresAt = validateExpiresAt(req.expiresAt, false);
+
+  const db = getDb();
+  const id = generateSnowflake();
+  const token = generateInviteToken();
+  const now = Date.now();
+
+  db.insert(schema.inviteLinks).values({
+    id,
+    token,
+    name,
+    createdBy: creatorId,
+    createdAt: now,
+    maxUses,
+    usedCount: 0,
+    expiresAt,
+    revokedAt: null,
+  }).run();
+
+  const row = db.select().from(schema.inviteLinks).where(eq(schema.inviteLinks.id, id)).get();
+  if (!row) throw new Error('Failed to insert invite');
+  return rowToSummary(row, resolveCreatorUsername(creatorId));
+}
+
+/**
+ * Look up the raw `invite_links` row by token. Used by the registration flow
+ * (check-invite, register) — those sites do their own derived-status checks.
+ * The format guard short-circuits before hitting the DB to keep malformed
+ * tokens cheap.
+ */
+export function getInviteByToken(token: string): typeof schema.inviteLinks.$inferSelect | null {
+  if (typeof token !== 'string' || !/^[A-Za-z0-9_-]{22}$/.test(token)) return null;
+  const db = getDb();
+  const row = db.select().from(schema.inviteLinks).where(eq(schema.inviteLinks.token, token)).get();
+  return row ?? null;
+}