diff --git a/.github/PULL_REQUEST_TEMPLATE.md b/.github/PULL_REQUEST_TEMPLATE.md
new file mode 100644
index 0000000..844bc9b
--- /dev/null
+++ b/.github/PULL_REQUEST_TEMPLATE.md
@@ -0,0 +1,24 @@
+## Summary
+
+<!-- 1-3 bullet points explaining what this PR does and why -->
+
+## Changes
+
+<!-- Describe the changes made in this PR -->
+
+## Testing
+
+<!-- How was this tested? What test cases were added/updated? -->
+
+## Checklist
+
+- [ ] **Tests added or updated** — Pure-function tests in `lib/__tests__/*.test.ts` follow `lib/__tests__/format.test.ts` pattern; component tests in `components/**/*.test.tsx` use `@testing-library/react` with `screen.getByRole()` for accessibility-first assertions
+- [ ] **Accessible interactive elements** — New interactive elements (buttons, inputs, links, menus) have appropriate ARIA roles and accessible names; verified via `screen.getByRole()` in tests
+- [ ] **Typecheck passes** — `npm run typecheck` produces no errors
+- [ ] **Lint passes** — `npm run lint` produces no errors
+- [ ] **Tests pass** — `npm test` passes, new tests verify the change works
+- [ ] **Build succeeds** — `npm run build` completes without errors
+
+## Notes
+
+<!-- Optional: any blockers, assumptions, or follow-up work -->
diff --git a/lib/__tests__/api.test.ts b/lib/__tests__/api.test.ts
new file mode 100644
index 0000000..fecbdee
--- /dev/null
+++ b/lib/__tests__/api.test.ts
@@ -0,0 +1,111 @@
+import { api } from "@/lib/api";
+
+// Mock fetch globally
+global.fetch = jest.fn();
+
+describe("api client error handling", () => {
+  beforeEach(() => {
+    (global.fetch as jest.Mock).mockClear();
+  });
+
+  // ---------------------------------------------------------------------------
+  // Non-200 response handling
+  // ---------------------------------------------------------------------------
+
+  it("returns null for non-200 responses", async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: false,
+      status: 404,
+    });
+
+    const result = await api.getStats();
+    expect(result).toBeNull();
+  });
+
+  it("returns null for 500 server errors", async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: false,
+      status: 500,
+    });
+
+    const result = await api.getStats();
+    expect(result).toBeNull();
+  });
+
+  it("handles 401 unauthorized without throwing", async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: false,
+      status: 401,
+    });
+
+    const result = await api.getStats();
+    expect(result).toBeNull();
+  });
+
+  // ---------------------------------------------------------------------------
+  // Malformed response body handling
+  // ---------------------------------------------------------------------------
+
+  it("throws error when response body is not valid JSON", async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      json: jest.fn().mockRejectedValueOnce(new SyntaxError("Unexpected token < in JSON at position 0")),
+    });
+
+    // This test documents the current buggy behavior: malformed JSON causes unhandled error
+    await expect(api.getStats()).rejects.toThrow(SyntaxError);
+  });
+
+  it("throws error when response body claims JSON but contains HTML (e.g., error page)", async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      json: jest.fn().mockRejectedValueOnce(new SyntaxError("Unexpected token < in JSON at position 0")),
+    });
+
+    await expect(api.getStats()).rejects.toThrow(SyntaxError);
+  });
+
+  it("throws error for unexpectedly-shaped JSON response", async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      json: jest.fn().mockResolvedValueOnce({ unexpected: "shape" }),
+    });
+
+    // Current behavior: no validation of response shape, just passes through
+    const result = await api.getStats();
+    // Type-wise this is { unexpected: "shape" } not ApiStatsResult, but no runtime error
+    expect(result).toEqual({ unexpected: "shape" });
+  });
+
+  // ---------------------------------------------------------------------------
+  // Successful responses
+  // ---------------------------------------------------------------------------
+
+  it("returns parsed JSON for successful response", async () => {
+    const mockData = {
+      totalAssets: 10,
+      tvl: "1000000000",
+      totalHolders: 250,
+    };
+
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      ok: true,
+      json: jest.fn().mockResolvedValueOnce(mockData),
+    });
+
+    const result = await api.getStats();
+    expect(result).toEqual(mockData);
+  });
+
+  it("returns null when URL is empty", async () => {
+    // When BASE is not set, apiUrl returns empty string
+    const originalEnv = process.env.NEXT_PUBLIC_API_URL;
+    delete process.env.NEXT_PUBLIC_API_URL;
+
+    const result = await api.getStats();
+    expect(result).toBeNull();
+    expect(global.fetch).not.toHaveBeenCalled();
+
+    process.env.NEXT_PUBLIC_API_URL = originalEnv;
+  });
+});
diff --git a/lib/__tests__/display.test.ts b/lib/__tests__/display.test.ts
new file mode 100644
index 0000000..fc2f324
--- /dev/null
+++ b/lib/__tests__/display.test.ts
@@ -0,0 +1,174 @@
+import { sanitizeDisplayText, getDisplayText } from "@/lib/display";
+
+// ---------------------------------------------------------------------------
+// sanitizeDisplayText — truncation, sanitization, and edge cases
+// ---------------------------------------------------------------------------
+describe("sanitizeDisplayText", () => {
+  // --- character and tag removal -------------------------------------------
+
+  it("removes control characters (0x00-0x1F, 0x7F)", () => {
+    const input = "Hello\x00World\x1FTest";
+    expect(sanitizeDisplayText(input)).toBe("HelloWorldTest");
+  });
+
+  it("removes HTML tags", () => {
+    expect(sanitizeDisplayText("<p>Hello</p> <b>World</b>")).toBe("Hello World");
+  });
+
+  it("removes script tags and their content interpretation", () => {
+    const input = "Safe<script>alert('xss')</script>Text";
+    expect(sanitizeDisplayText(input)).toBe("SafeText");
+  });
+
+  it("normalizes multiple spaces to single space", () => {
+    expect(sanitizeDisplayText("Hello    World   Test")).toBe("Hello World Test");
+  });
+
+  // --- truncation by length ------------------------------------------------
+
+  it("truncates text longer than maxLength to specified length", () => {
+    const longText = "a".repeat(250);
+    const result = sanitizeDisplayText(longText, { maxLength: 220 });
+    expect(result.length).toBe(221); // 220 chars + "…" ellipsis
+    expect(result.endsWith("…")).toBe(true);
+  });
+
+  it("uses default maxLength of 220 when not specified", () => {
+    const longText = "x".repeat(250);
+    const result = sanitizeDisplayText(longText);
+    expect(result.length).toBe(221); // 220 + "…"
+  });
+
+  it("does not add ellipsis if text is shorter than maxLength", () => {
+    const text = "Short text";
+    expect(sanitizeDisplayText(text, { maxLength: 220 })).toBe("Short text");
+    expect(sanitizeDisplayText(text)).toBe("Short text");
+  });
+
+  it("trims trailing whitespace before adding ellipsis", () => {
+    const text = "a".repeat(220) + "   ";
+    const result = sanitizeDisplayText(text, { maxLength: 220 });
+    expect(result).toBe("a".repeat(220) + "…");
+    expect(result).not.toMatch(/\s…$/);
+  });
+
+  // --- truncation by line count --------------------------------------------
+
+  it("collapses lines to maxLines (default 8)", () => {
+    const nineLines = "line1\nline2\nline3\nline4\nline5\nline6\nline7\nline8\nline9";
+    const result = sanitizeDisplayText(nineLines);
+    const lineCount = result.split("\n").length;
+    expect(lineCount).toBe(8);
+  });
+
+  it("preserves lines up to maxLines", () => {
+    const threeLines = "line1\nline2\nline3";
+    expect(sanitizeDisplayText(threeLines, { maxLines: 3 })).toBe("line1\nline2\nline3");
+  });
+
+  it("trims each line individually", () => {
+    const input = "  line1  \n  line2  \n  line3  ";
+    const result = sanitizeDisplayText(input, { maxLines: 3 });
+    const lines = result.split("\n");
+    expect(lines[0]).toBe("line1");
+    expect(lines[1]).toBe("line2");
+    expect(lines[2]).toBe("line3");
+  });
+
+  it("filters out empty lines", () => {
+    const input = "line1\n\n\nline2\n";
+    const result = sanitizeDisplayText(input, { maxLines: 10 });
+    expect(result).toBe("line1\nline2");
+  });
+
+  // --- empty and short input -----------------------------------------------
+
+  it("returns empty string for null input", () => {
+    expect(sanitizeDisplayText(null)).toBe("");
+  });
+
+  it("returns empty string for undefined input", () => {
+    expect(sanitizeDisplayText(undefined)).toBe("");
+  });
+
+  it("returns empty string for whitespace-only input", () => {
+    expect(sanitizeDisplayText("   \n\n  ")).toBe("");
+  });
+
+  it("handles single character input", () => {
+    expect(sanitizeDisplayText("a")).toBe("a");
+  });
+
+  it("handles single-character input at truncation boundary", () => {
+    // Single char should not be truncated
+    const result = sanitizeDisplayText("x", { maxLength: 5 });
+    expect(result).toBe("x");
+  });
+
+  // --- combined scenarios --------------------------------------------------
+
+  it("truncates by length and line count together", () => {
+    const input = "a".repeat(300) + "\nline2\nline3\nline4\nline5\nline6\nline7\nline8\nline9";
+    const result = sanitizeDisplayText(input, { maxLength: 220, maxLines: 5 });
+    expect(result.split("\n").length).toBe(5);
+    expect(result).toContain("…");
+  });
+
+  it("handles text with tags, control chars, and truncation", () => {
+    const input = "<p>Hello\x00World</p>" + "x".repeat(250);
+    const result = sanitizeDisplayText(input, { maxLength: 50 });
+    expect(result).toMatch(/^Hello World/);
+    expect(result.length).toBe(51); // 50 + "…"
+    expect(result).toContain("…");
+  });
+
+  it("normalizes whitespace after removing tags", () => {
+    const input = "Hello<br/>  \n\n  World";
+    expect(sanitizeDisplayText(input)).toBe("Hello World");
+  });
+});
+
+// ---------------------------------------------------------------------------
+// getDisplayText — wrapper with fallback
+// ---------------------------------------------------------------------------
+describe("getDisplayText", () => {
+  it("returns sanitized text when text is non-empty", () => {
+    expect(getDisplayText("Hello World")).toBe("Hello World");
+  });
+
+  it("returns fallback when text is null", () => {
+    expect(getDisplayText(null)).toBe("Untitled");
+  });
+
+  it("returns fallback when text is undefined", () => {
+    expect(getDisplayText(undefined)).toBe("Untitled");
+  });
+
+  it("returns fallback when text is empty string", () => {
+    expect(getDisplayText("")).toBe("Untitled");
+  });
+
+  it("returns fallback when text is whitespace-only", () => {
+    expect(getDisplayText("   \n  ")).toBe("Untitled");
+  });
+
+  it("uses custom fallback when provided", () => {
+    expect(getDisplayText(null, "No Title")).toBe("No Title");
+    expect(getDisplayText("", "Custom Default")).toBe("Custom Default");
+  });
+
+  it("applies sanitization and uses fallback independently", () => {
+    expect(getDisplayText("<p></p>", "Empty")).toBe("Empty");
+    expect(getDisplayText("<p>Content</p>")).toBe("Content");
+  });
+
+  it("sanitizes text before checking for fallback", () => {
+    const allTags = "<p></p><div></div>";
+    expect(getDisplayText(allTags)).toBe("Untitled");
+  });
+
+  it("preserves structure after sanitization", () => {
+    const result = getDisplayText("Line1\nLine2\nLine3");
+    expect(result).toBe("Line1\nLine2\nLine3");
+  });
+});