diff --git a/src/lib/__tests__/invoiceTags.test.ts b/src/lib/__tests__/invoiceTags.test.ts
new file mode 100644
index 0000000..6e9a9cb
--- /dev/null
+++ b/src/lib/__tests__/invoiceTags.test.ts
@@ -0,0 +1,109 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import {
+  filterByTags,
+  setTags,
+  getTags,
+  __resetTagStore,
+  normalizeTag,
+  normalizeTags,
+  invoiceHasTag,
+} from "../invoiceTags";
+import type { Invoice } from "@stellar-split/sdk";
+
+function createMockInvoice(id: string, tags?: string[]): Invoice {
+  return {
+    id,
+    creator: "GCREATOR",
+    recipients: [{ address: "GRECIPIENT", amount: 1000n }],
+    token: "CDREXAMPLE",
+    deadline: Math.floor(Date.now() / 1000) + 3600,
+    funded: 0n,
+    status: "Pending",
+    payments: [],
+    ...(tags ? { tags } : {}),
+  } as unknown as Invoice;
+}
+
+describe("invoiceTags", () => {
+  beforeEach(() => {
+    __resetTagStore();
+  });
+
+  describe("filterByTags", () => {
+    const inv1 = createMockInvoice("inv-1"); // tags: ["urgent", "operations"]
+    const inv2 = createMockInvoice("inv-2"); // tags: ["operations", "audit"]
+    const inv3 = createMockInvoice("inv-3"); // tags: ["marketing"]
+    const inv4 = createMockInvoice("inv-4"); // tags: []
+
+    beforeEach(() => {
+      setTags("inv-1", ["urgent", "operations"]);
+      setTags("inv-2", ["operations", "audit"]);
+      setTags("inv-3", ["marketing"]);
+      setTags("inv-4", []);
+    });
+
+    it("returns all invoices unchanged when tags array is empty", () => {
+      const invoices = [inv1, inv2, inv3, inv4];
+      const result = filterByTags(invoices, []);
+      expect(result).toEqual(invoices);
+    });
+
+    it("returns all invoices unchanged when tags only contain whitespace or empty strings", () => {
+      const invoices = [inv1, inv2, inv3, inv4];
+      const result = filterByTags(invoices, ["   ", ""]);
+      expect(result).toEqual(invoices);
+    });
+
+    it("filters with any-match (default matchAll: false)", () => {
+      const invoices = [inv1, inv2, inv3, inv4];
+      const result = filterByTags(invoices, ["urgent", "marketing"]);
+      expect(result.map((i) => i.id)).toEqual(["inv-1", "inv-3"]);
+    });
+
+    it("filters with all-match (matchAll: true)", () => {
+      const invoices = [inv1, inv2, inv3, inv4];
+      const result = filterByTags(invoices, ["urgent", "operations"], { matchAll: true });
+      expect(result.map((i) => i.id)).toEqual(["inv-1"]);
+    });
+
+    it("returns empty array when no invoices match", () => {
+      const invoices = [inv1, inv2, inv3, inv4];
+      const result = filterByTags(invoices, ["nonexistent-tag"]);
+      expect(result).toEqual([]);
+    });
+
+    it("is case-insensitive and normalizes whitespace in search tags", () => {
+      const invoices = [inv1, inv2, inv3, inv4];
+      const result = filterByTags(invoices, ["  URGENT  "]);
+      expect(result.map((i) => i.id)).toEqual(["inv-1"]);
+    });
+
+    it("works with tags directly attached to the invoice object", () => {
+      const attached1 = createMockInvoice("custom-1", ["finance", "tax"]);
+      const attached2 = createMockInvoice("custom-2", ["tax"]);
+      const attached3 = createMockInvoice("custom-3", ["engineering"]);
+
+      const list = [attached1, attached2, attached3];
+      const anyTax = filterByTags(list, ["tax"]);
+      expect(anyTax.map((i) => i.id)).toEqual(["custom-1", "custom-2"]);
+
+      const allTaxFinance = filterByTags(list, ["tax", "finance"], { matchAll: true });
+      expect(allTaxFinance.map((i) => i.id)).toEqual(["custom-1"]);
+    });
+  });
+
+  describe("normalization & lookup", () => {
+    it("normalizes single tag", () => {
+      expect(normalizeTag("  HELLO   World  ")).toBe("hello world");
+    });
+
+    it("normalizes tag list and drops duplicates", () => {
+      expect(normalizeTags(["tag1", "TAG1", "  tag2  ", ""])).toEqual(["tag1", "tag2"]);
+    });
+
+    it("checks tag presence case-insensitively", () => {
+      expect(invoiceHasTag(["Product", "Design"], "product")).toBe(true);
+      expect(invoiceHasTag(["Product", "Design"], "marketing")).toBe(false);
+    });
+  });
+});
diff --git a/src/lib/invoiceTags.ts b/src/lib/invoiceTags.ts
index e70026a..1079f18 100644
--- a/src/lib/invoiceTags.ts
+++ b/src/lib/invoiceTags.ts
@@ -6,6 +6,7 @@
  * id — the same approach `api/invoices/[id]/route.ts` uses for splitMeta.
  */
 import { z } from "zod";
+import type { Invoice } from "@stellar-split/sdk";
 
 export const MAX_TAG_LENGTH = 32;
 export const MAX_TAGS_PER_INVOICE = 20;
@@ -150,3 +151,42 @@ export function tagColorClass(tag: string): string {
   }
   return TAG_COLORS[hash % TAG_COLORS.length];
 }
+
+export interface FilterByTagsOptions {
+  matchAll?: boolean;
+}
+
+/**
+ * Filters a list of invoices by one or more tags.
+ * - Empty `tags` array returns all invoices unchanged.
+ * - Default (`matchAll: false`): returns invoices that have any of the given tags.
+ * - `matchAll: true`: returns only invoices that have all of the given tags.
+ */
+export function filterByTags(
+  invoices: Invoice[],
+  tags: string[],
+  opts: FilterByTagsOptions = {},
+): Invoice[] {
+  if (!tags || tags.length === 0) {
+    return invoices;
+  }
+
+  const { matchAll = false } = opts;
+  const targetTags = tags.map((t) => normalizeTag(t)).filter(Boolean);
+
+  if (targetTags.length === 0) {
+    return invoices;
+  }
+
+  return invoices.filter((invoice) => {
+    const attachedTags = (invoice as { tags?: readonly string[] }).tags;
+    const invTags = Array.isArray(attachedTags) ? attachedTags : getTags(invoice.id);
+
+    if (matchAll) {
+      return targetTags.every((target) => invoiceHasTag(invTags, target));
+    } else {
+      return targetTags.some((target) => invoiceHasTag(invTags, target));
+    }
+  });
+}
+