diff --git a/src/lib/timeline-db.ts b/src/lib/timeline-db.ts
index 49b4f78..9e5a932 100644
--- a/src/lib/timeline-db.ts
+++ b/src/lib/timeline-db.ts
@@ -289,13 +289,43 @@ export async function insertEvents(events: TimelineEvent[], projectDir?: string)
   }
 }
 
-function buildWhereFilter(opts: SearchOptions): string | undefined {
+/** Escape single quotes for safe use in SQL string literals */
+export function escapeSQL(value: string): string {
+  return value.replace(/'/g, "''");
+}
+
+/** Validate that a value matches expected EVENT_TYPES to prevent injection */
+export function isValidEventType(value: string): value is EventType {
+  return (EVENT_TYPES as readonly string[]).includes(value);
+}
+
+/** Validate ISO-8601 timestamp format */
+export function isValidTimestamp(value: string): boolean {
+  return /^\d{4}-\d{2}-\d{2}(T\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[+-]\d{2}:?\d{2})?)?$/.test(value);
+}
+
+export function buildWhereFilter(opts: SearchOptions): string | undefined {
   const clauses: string[] = [];
-  if (opts.project) clauses.push(`project = '${opts.project}'`);
-  if (opts.branch) clauses.push(`branch = '${opts.branch}'`);
-  if (opts.type) clauses.push(`type = '${opts.type}'`);
-  if (opts.since) clauses.push(`timestamp >= '${opts.since}'`);
-  if (opts.until) clauses.push(`timestamp <= '${opts.until}'`);
+  if (opts.project) clauses.push(`project = '${escapeSQL(opts.project)}'`);
+  if (opts.branch) clauses.push(`branch = '${escapeSQL(opts.branch)}'`);
+  if (opts.type) {
+    if (!isValidEventType(opts.type)) {
+      throw new Error(`Invalid event type: ${opts.type}`);
+    }
+    clauses.push(`type = '${opts.type}'`);
+  }
+  if (opts.since) {
+    if (!isValidTimestamp(opts.since)) {
+      throw new Error(`Invalid timestamp for 'since': ${opts.since}`);
+    }
+    clauses.push(`timestamp >= '${opts.since}'`);
+  }
+  if (opts.until) {
+    if (!isValidTimestamp(opts.until)) {
+      throw new Error(`Invalid timestamp for 'until': ${opts.until}`);
+    }
+    clauses.push(`timestamp <= '${opts.until}'`);
+  }
   return clauses.length > 0 ? clauses.join(" AND ") : undefined;
 }
 
@@ -358,7 +388,7 @@ export async function searchExact(
   opts: SearchOptions = {},
 ): Promise<TimelineRecord[]> {
   const limit = opts.limit || 50;
-  const likeClauses = [`content LIKE '%${query.replace(/'/g, "''")}%'`];
+  const likeClauses = [`content LIKE '%${escapeSQL(query)}%'`];
   const where = buildWhereFilter(opts);
   const fullWhere = where ? `${likeClauses[0]} AND ${where}` : likeClauses[0];
 
diff --git a/tests/lib/timeline-db.test.ts b/tests/lib/timeline-db.test.ts
new file mode 100644
index 0000000..4837b9a
--- /dev/null
+++ b/tests/lib/timeline-db.test.ts
@@ -0,0 +1,120 @@
+import { describe, it, expect } from "vitest";
+import {
+  escapeSQL,
+  isValidEventType,
+  isValidTimestamp,
+  buildWhereFilter,
+  EVENT_TYPES,
+} from "../../src/lib/timeline-db.js";
+
+describe("escapeSQL", () => {
+  it("escapes single quotes", () => {
+    expect(escapeSQL("it's")).toBe("it''s");
+  });
+
+  it("escapes multiple single quotes", () => {
+    expect(escapeSQL("it's a 'test'")).toBe("it''s a ''test''");
+  });
+
+  it("passes through safe strings", () => {
+    expect(escapeSQL("hello world")).toBe("hello world");
+  });
+
+  it("handles empty string", () => {
+    expect(escapeSQL("")).toBe("");
+  });
+});
+
+describe("isValidEventType", () => {
+  it("accepts all valid event types", () => {
+    for (const t of EVENT_TYPES) {
+      expect(isValidEventType(t)).toBe(true);
+    }
+  });
+
+  it("rejects invalid types", () => {
+    expect(isValidEventType("invalid")).toBe(false);
+    expect(isValidEventType("' OR 1=1 --")).toBe(false);
+    expect(isValidEventType("")).toBe(false);
+  });
+});
+
+describe("isValidTimestamp", () => {
+  it("accepts valid ISO timestamps", () => {
+    expect(isValidTimestamp("2024-01-15")).toBe(true);
+    expect(isValidTimestamp("2024-01-15T10:30:00Z")).toBe(true);
+    expect(isValidTimestamp("2024-01-15T10:30:00.123Z")).toBe(true);
+    expect(isValidTimestamp("2024-01-15T10:30:00+05:30")).toBe(true);
+    expect(isValidTimestamp("2024-01-15T10:30:00-08:00")).toBe(true);
+  });
+
+  it("rejects invalid timestamps", () => {
+    expect(isValidTimestamp("not-a-date")).toBe(false);
+    expect(isValidTimestamp("' OR 1=1 --")).toBe(false);
+    expect(isValidTimestamp("2024/01/15")).toBe(false);
+    expect(isValidTimestamp("")).toBe(false);
+  });
+});
+
+describe("buildWhereFilter", () => {
+  it("returns undefined for empty options", () => {
+    expect(buildWhereFilter({})).toBeUndefined();
+  });
+
+  it("builds single project filter", () => {
+    expect(buildWhereFilter({ project: "/my/project" })).toBe(
+      "project = '/my/project'"
+    );
+  });
+
+  it("escapes quotes in project path", () => {
+    expect(buildWhereFilter({ project: "it's/a/path" })).toBe(
+      "project = 'it''s/a/path'"
+    );
+  });
+
+  it("escapes quotes in branch name", () => {
+    expect(buildWhereFilter({ branch: "fix/it's-broken" })).toBe(
+      "branch = 'fix/it''s-broken'"
+    );
+  });
+
+  it("combines multiple filters with AND", () => {
+    const result = buildWhereFilter({
+      project: "/proj",
+      branch: "main",
+      type: "prompt",
+    });
+    expect(result).toBe(
+      "project = '/proj' AND branch = 'main' AND type = 'prompt'"
+    );
+  });
+
+  it("throws on invalid event type", () => {
+    expect(() => buildWhereFilter({ type: "malicious' OR 1=1 --" as any })).toThrow(
+      "Invalid event type"
+    );
+  });
+
+  it("throws on invalid since timestamp", () => {
+    expect(() => buildWhereFilter({ since: "'; DROP TABLE events; --" })).toThrow(
+      "Invalid timestamp"
+    );
+  });
+
+  it("throws on invalid until timestamp", () => {
+    expect(() => buildWhereFilter({ until: "not-a-date" })).toThrow(
+      "Invalid timestamp"
+    );
+  });
+
+  it("accepts valid timestamp range", () => {
+    const result = buildWhereFilter({
+      since: "2024-01-01T00:00:00Z",
+      until: "2024-12-31T23:59:59Z",
+    });
+    expect(result).toBe(
+      "timestamp >= '2024-01-01T00:00:00Z' AND timestamp <= '2024-12-31T23:59:59Z'"
+    );
+  });
+});