diff --git a/src/cliproxy/binary/downloader.ts b/src/cliproxy/binary/downloader.ts
index 500b673f..e34c5490 100644
--- a/src/cliproxy/binary/downloader.ts
+++ b/src/cliproxy/binary/downloader.ts
@@ -539,3 +539,11 @@ export async function fetchJson(
 function sleep(ms: number): Promise<void> {
   return new Promise((resolve) => setTimeout(resolve, ms));
 }
+
+// Export internal functions for testing
+export const __testExports = {
+  getProxyUrl,
+  shouldBypassProxy,
+  getHostname,
+  getProxyAgent,
+};
diff --git a/tests/unit/cliproxy/binary-downloader-proxy.test.ts b/tests/unit/cliproxy/binary-downloader-proxy.test.ts
new file mode 100644
index 00000000..a92926f5
--- /dev/null
+++ b/tests/unit/cliproxy/binary-downloader-proxy.test.ts
@@ -0,0 +1,260 @@
+/**
+ * Binary Downloader Proxy Support Tests
+ *
+ * Tests for proxy environment variable detection and NO_PROXY bypass logic.
+ */
+
+import { describe, it, expect, beforeEach, afterEach } from 'bun:test';
+import { __testExports } from '../../../src/cliproxy/binary/downloader';
+
+const { getProxyUrl, shouldBypassProxy, getHostname, getProxyAgent } = __testExports;
+
+describe('Binary Downloader Proxy Support', () => {
+  // Store original env vars to restore after tests
+  const originalEnv: Record<string, string | undefined> = {};
+  const proxyEnvVars = [
+    'http_proxy',
+    'HTTP_PROXY',
+    'https_proxy',
+    'HTTPS_PROXY',
+    'all_proxy',
+    'ALL_PROXY',
+    'no_proxy',
+    'NO_PROXY',
+  ];
+
+  beforeEach(() => {
+    // Save original values
+    proxyEnvVars.forEach((key) => {
+      originalEnv[key] = process.env[key];
+      delete process.env[key];
+    });
+  });
+
+  afterEach(() => {
+    // Restore original values
+    proxyEnvVars.forEach((key) => {
+      if (originalEnv[key] !== undefined) {
+        process.env[key] = originalEnv[key];
+      } else {
+        delete process.env[key];
+      }
+    });
+  });
+
+  describe('getProxyUrl', () => {
+    describe('HTTPS requests', () => {
+      it('should return undefined when no proxy env vars are set', () => {
+        expect(getProxyUrl(true)).toBeUndefined();
+      });
+
+      it('should prefer https_proxy (lowercase)', () => {
+        process.env.https_proxy = 'http://proxy1:8080';
+        process.env.HTTPS_PROXY = 'http://proxy2:8080';
+        expect(getProxyUrl(true)).toBe('http://proxy1:8080');
+      });
+
+      it('should fall back to HTTPS_PROXY (uppercase)', () => {
+        process.env.HTTPS_PROXY = 'http://proxy:8080';
+        expect(getProxyUrl(true)).toBe('http://proxy:8080');
+      });
+
+      it('should fall back to all_proxy', () => {
+        process.env.all_proxy = 'http://allproxy:8080';
+        expect(getProxyUrl(true)).toBe('http://allproxy:8080');
+      });
+
+      it('should fall back to ALL_PROXY', () => {
+        process.env.ALL_PROXY = 'http://allproxy:8080';
+        expect(getProxyUrl(true)).toBe('http://allproxy:8080');
+      });
+    });
+
+    describe('HTTP requests', () => {
+      it('should return undefined when no proxy env vars are set', () => {
+        expect(getProxyUrl(false)).toBeUndefined();
+      });
+
+      it('should prefer http_proxy (lowercase)', () => {
+        process.env.http_proxy = 'http://proxy1:8080';
+        process.env.HTTP_PROXY = 'http://proxy2:8080';
+        expect(getProxyUrl(false)).toBe('http://proxy1:8080');
+      });
+
+      it('should fall back to HTTP_PROXY (uppercase)', () => {
+        process.env.HTTP_PROXY = 'http://proxy:8080';
+        expect(getProxyUrl(false)).toBe('http://proxy:8080');
+      });
+
+      it('should fall back to all_proxy for HTTP', () => {
+        process.env.all_proxy = 'http://allproxy:8080';
+        expect(getProxyUrl(false)).toBe('http://allproxy:8080');
+      });
+
+      it('should not use https_proxy for HTTP requests', () => {
+        process.env.https_proxy = 'http://httpsproxy:8080';
+        expect(getProxyUrl(false)).toBeUndefined();
+      });
+    });
+  });
+
+  describe('shouldBypassProxy', () => {
+    describe('when NO_PROXY is not set', () => {
+      it('should return false', () => {
+        expect(shouldBypassProxy('example.com')).toBe(false);
+      });
+    });
+
+    describe('wildcard pattern', () => {
+      it('should bypass all hosts with *', () => {
+        process.env.NO_PROXY = '*';
+        expect(shouldBypassProxy('example.com')).toBe(true);
+        expect(shouldBypassProxy('any.host.here')).toBe(true);
+      });
+    });
+
+    describe('exact match', () => {
+      it('should match exact hostname', () => {
+        process.env.NO_PROXY = 'example.com';
+        expect(shouldBypassProxy('example.com')).toBe(true);
+        expect(shouldBypassProxy('other.com')).toBe(false);
+      });
+
+      it('should be case-insensitive', () => {
+        process.env.NO_PROXY = 'Example.COM';
+        expect(shouldBypassProxy('example.com')).toBe(true);
+        expect(shouldBypassProxy('EXAMPLE.COM')).toBe(true);
+      });
+
+      it('should not match subdomains for exact pattern', () => {
+        process.env.NO_PROXY = 'example.com';
+        expect(shouldBypassProxy('sub.example.com')).toBe(true); // matches as suffix
+        expect(shouldBypassProxy('notexample.com')).toBe(false);
+      });
+    });
+
+    describe('domain suffix pattern', () => {
+      it('should match subdomains with leading dot', () => {
+        process.env.NO_PROXY = '.example.com';
+        expect(shouldBypassProxy('sub.example.com')).toBe(true);
+        expect(shouldBypassProxy('deep.sub.example.com')).toBe(true);
+        expect(shouldBypassProxy('example.com')).toBe(true); // exact match without dot
+      });
+
+      it('should not match different domains', () => {
+        process.env.NO_PROXY = '.example.com';
+        expect(shouldBypassProxy('notexample.com')).toBe(false);
+        expect(shouldBypassProxy('example.org')).toBe(false);
+      });
+    });
+
+    describe('multiple patterns', () => {
+      it('should check comma-separated list', () => {
+        process.env.NO_PROXY = 'localhost,127.0.0.1,.internal.corp';
+        expect(shouldBypassProxy('localhost')).toBe(true);
+        expect(shouldBypassProxy('127.0.0.1')).toBe(true);
+        expect(shouldBypassProxy('api.internal.corp')).toBe(true);
+        expect(shouldBypassProxy('external.com')).toBe(false);
+      });
+
+      it('should handle whitespace in list', () => {
+        process.env.NO_PROXY = ' localhost , example.com , .corp ';
+        expect(shouldBypassProxy('localhost')).toBe(true);
+        expect(shouldBypassProxy('example.com')).toBe(true);
+        expect(shouldBypassProxy('host.corp')).toBe(true);
+      });
+    });
+
+    describe('lowercase no_proxy', () => {
+      it('should respect no_proxy (lowercase)', () => {
+        process.env.no_proxy = 'example.com';
+        expect(shouldBypassProxy('example.com')).toBe(true);
+      });
+
+      it('should prefer no_proxy over NO_PROXY', () => {
+        process.env.no_proxy = 'lower.com';
+        process.env.NO_PROXY = 'upper.com';
+        expect(shouldBypassProxy('lower.com')).toBe(true);
+        expect(shouldBypassProxy('upper.com')).toBe(false);
+      });
+    });
+  });
+
+  describe('getHostname', () => {
+    it('should extract hostname from HTTPS URL', () => {
+      expect(getHostname('https://example.com/path')).toBe('example.com');
+    });
+
+    it('should extract hostname from HTTP URL', () => {
+      expect(getHostname('http://api.github.com:443/repos')).toBe('api.github.com');
+    });
+
+    it('should return empty string for invalid URL', () => {
+      expect(getHostname('not-a-url')).toBe('');
+      expect(getHostname('')).toBe('');
+    });
+
+    it('should handle localhost', () => {
+      expect(getHostname('http://localhost:8080')).toBe('localhost');
+    });
+
+    it('should handle IP addresses', () => {
+      expect(getHostname('http://192.168.1.1:3000')).toBe('192.168.1.1');
+    });
+  });
+
+  describe('getProxyAgent', () => {
+    describe('when no proxy is configured', () => {
+      it('should return false for HTTPS URLs', () => {
+        expect(getProxyAgent('https://example.com')).toBe(false);
+      });
+
+      it('should return false for HTTP URLs', () => {
+        expect(getProxyAgent('http://example.com')).toBe(false);
+      });
+    });
+
+    describe('when proxy is configured', () => {
+      it('should return HttpsProxyAgent for HTTPS URLs', () => {
+        process.env.https_proxy = 'http://proxy:8080';
+        const agent = getProxyAgent('https://github.com/releases');
+        expect(agent).not.toBe(false);
+        expect(agent).toBeDefined();
+      });
+
+      it('should return HttpProxyAgent for HTTP URLs', () => {
+        process.env.http_proxy = 'http://proxy:8080';
+        const agent = getProxyAgent('http://example.com');
+        expect(agent).not.toBe(false);
+        expect(agent).toBeDefined();
+      });
+    });
+
+    describe('NO_PROXY bypass', () => {
+      it('should bypass proxy for NO_PROXY hosts', () => {
+        process.env.https_proxy = 'http://proxy:8080';
+        process.env.NO_PROXY = 'github.com';
+        expect(getProxyAgent('https://github.com/releases')).toBe(false);
+      });
+
+      it('should use proxy for non-bypassed hosts', () => {
+        process.env.https_proxy = 'http://proxy:8080';
+        process.env.NO_PROXY = 'internal.corp';
+        const agent = getProxyAgent('https://github.com/releases');
+        expect(agent).not.toBe(false);
+      });
+    });
+
+    describe('error handling', () => {
+      it('should return false for invalid proxy URL', () => {
+        process.env.https_proxy = 'not-a-valid-url';
+        expect(getProxyAgent('https://example.com')).toBe(false);
+      });
+
+      it('should return false for invalid target URL', () => {
+        process.env.https_proxy = 'http://proxy:8080';
+        expect(getProxyAgent('not-a-url')).toBe(false);
+      });
+    });
+  });
+});