diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e8aef8aa..5c67a0ea 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -215,7 +215,7 @@ To debug the CLI's React-based UI, you can use React DevTools. Ink, the library
 
 ### MacOS Seatbelt
 
-On MacOS, `gemini` uses Seatbelt (`sandbox-exec`) under a `minimal` profile (see `packages/cli/src/utils/sandbox-macos-minimal.sb`) that restricts writes to the project folder but otherwise allows all other operations by default. You can switch to a `strict` profile (see `.../sandbox-macos-strict.sb`) that declines operations by default by setting `SEATBELT_PROFILE=strict` in your environment or `.env` file. You can also switch to a custom profile `SEATBELT_PROFILE=<profile>` if you also create a file `.gemini/sandbox-macos-<profile>.sb` under your project settings directory `.gemini`.
+On MacOS, `gemini` uses Seatbelt (`sandbox-exec`) under a `permissive-open` profile (see `packages/cli/src/utils/sandbox-macos-permissive-open.sb`) that restricts writes to the project folder but otherwise allows all other operations and outbound network traffic ("open") by default. You can switch to a `restrictive-closed` profile (see `.../sandbox-macos-strict.sb`) that declines all operations and outbound network traffic ("closed") by default by setting `SEATBELT_PROFILE=restrictive-closed` in your environment or `.env` file. Available built-in profiles are `{permissive,restrictive}-{open,closed,proxied}` (see below for proxied networking). You can also switch to a custom profile `SEATBELT_PROFILE=<profile>` if you also create a file `.gemini/sandbox-macos-<profile>.sb` under your project settings directory `.gemini`.
 
 ### Container-based Sandboxing (All Platforms)
 
@@ -223,6 +223,10 @@ For stronger container-based sandboxing on MacOS or other platforms, you can set
 
 Container-based sandboxing mounts the project directory (and system temp directory) with read-write access and is started/stopped/removed automatically as you start/stop Gemini CLI. Files created within the sandbox should be automatically mapped to your user/group on host machine. You can easily specify additional mounts, ports, or environment variables by setting `SANDBOX_{MOUNTS,PORTS,ENV}` as needed. You can also fully customize the sandbox for your projects by creating the files `.gemini/sandbox.Dockerfile` and/or `.gemini/sandbox.bashrc` under your project settings directory (`.gemini`) and running `gemini` with `BUILD_SANDBOX=1` to trigger building of your custom sandbox.
 
+#### Proxied Networking
+
+All sandboxing methods, including MacOS Seatbelt using `*-proxied` profiles, support restricting outbound network traffic through a custom proxy server that can be specified as `GEMINI_SANDBOX_PROXY_COMMAND=<command>`, where `<command>` must start a proxy server that listens on `0.0.0.0:8877` for relevant requests. See `scripts/example-proxy.js` for a minimal proxy that only allows `HTTPS` connections to `example.com:443` (e.g. `curl https://example.com`) and declines all other requests. The proxy is started and stopped automatically alongside the sandbox.
+
 ## Manual Publish
 
 We publish an artifact for each commit to our internal registry. But if you need to manually cut a local build, then run the following commands:
diff --git a/Dockerfile b/Dockerfile
index d6e8c2ae..092e1ed5 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -23,6 +23,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   psmisc \
   lsof \
   socat \
+  ca-certificates \
   && apt-get clean \
   && rm -rf /var/lib/apt/lists/*
 
diff --git a/docs/cli/configuration.md b/docs/cli/configuration.md
index 7c8ff81e..05dfc65b 100644
--- a/docs/cli/configuration.md
+++ b/docs/cli/configuration.md
@@ -203,7 +203,7 @@ The CLI automatically loads environment variables from an `.env` file. The loadi
   - Accepts `true`, `false`, `docker`, `podman`, or a custom command string.
 - **`SEATBELT_PROFILE`** (macOS specific):
   - Switches the Seatbelt (`sandbox-exec`) profile on macOS.
-  - `minimal`: (Default) Restricts writes to the project folder (and a few other folders, see `packages/cli/src/utils/sandbox-macos-minimal.sb`) but allows other operations.
+  - `permissive-open`: (Default) Restricts writes to the project folder (and a few other folders, see `packages/cli/src/utils/sandbox-macos-permissive-open.sb`) but allows other operations.
   - `strict`: Uses a strict profile that declines operations by default.
   - `<profile_name>`: Uses a custom profile. To define a custom profile, create a file named `sandbox-macos-<profile_name>.sb` in your project's `.gemini/` directory (e.g., `my-project/.gemini/sandbox-macos-custom.sb`).
 - **`DEBUG` or `DEBUG_MODE`** (often used by underlying libraries or the CLI itself):
diff --git a/package-lock.json b/package-lock.json
index becc665a..5c502b4a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9403,6 +9403,15 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/undici": {
+      "version": "7.10.0",
+      "resolved": "https://registry.npmjs.org/undici/-/undici-7.10.0.tgz",
+      "integrity": "sha512-u5otvFBOBZvmdjWLVW+5DAc9Nkq8f24g0O9oY7qw2JVIF1VocIFoyz9JFkuVOS2j41AufeO0xnlweJ2RLT8nGw==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=20.18.1"
+      }
+    },
     "node_modules/undici-types": {
       "version": "6.19.8",
       "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-6.19.8.tgz",
@@ -10754,7 +10763,8 @@
         "fast-glob": "^3.3.3",
         "ignore": "^7.0.0",
         "shell-quote": "^1.8.2",
-        "strip-ansi": "^7.1.0"
+        "strip-ansi": "^7.1.0",
+        "undici": "^7.10.0"
       },
       "devDependencies": {
         "@types/diff": "^7.0.2",
diff --git a/packages/cli/src/utils/sandbox-macos-permissive-closed.sb b/packages/cli/src/utils/sandbox-macos-permissive-closed.sb
new file mode 100644
index 00000000..36d88995
--- /dev/null
+++ b/packages/cli/src/utils/sandbox-macos-permissive-closed.sb
@@ -0,0 +1,26 @@
+(version 1)
+
+;; allow everything by default
+(allow default)
+
+;; deny all writes EXCEPT under specific paths
+(deny file-write*)
+(allow file-write*
+    (subpath (param "TARGET_DIR"))
+    (subpath (param "TMP_DIR"))
+    (subpath (param "CACHE_DIR"))
+    (subpath (string-append (param "HOME_DIR") "/.gemini"))
+    (subpath (string-append (param "HOME_DIR") "/.npm"))
+    (subpath (string-append (param "HOME_DIR") "/.cache"))
+    (subpath (string-append (param "HOME_DIR") "/.gitconfig"))
+    (literal "/dev/stdout")
+    (literal "/dev/stderr")
+    (literal "/dev/null")
+)
+
+;; deny all inbound network traffic EXCEPT on debugger port
+(deny network-inbound)
+(allow network-inbound (local ip "localhost:9229"))
+
+;; deny all outbound network traffic
+(deny network-outbound)
diff --git a/packages/cli/src/utils/sandbox-macos-minimal.sb b/packages/cli/src/utils/sandbox-macos-permissive-open.sb
similarity index 100%
rename from packages/cli/src/utils/sandbox-macos-minimal.sb
rename to packages/cli/src/utils/sandbox-macos-permissive-open.sb
diff --git a/packages/cli/src/utils/sandbox-macos-permissive-proxied.sb b/packages/cli/src/utils/sandbox-macos-permissive-proxied.sb
new file mode 100644
index 00000000..861e503d
--- /dev/null
+++ b/packages/cli/src/utils/sandbox-macos-permissive-proxied.sb
@@ -0,0 +1,31 @@
+(version 1)
+
+;; allow everything by default
+(allow default)
+
+;; deny all writes EXCEPT under specific paths
+(deny file-write*)
+(allow file-write*
+    (subpath (param "TARGET_DIR"))
+    (subpath (param "TMP_DIR"))
+    (subpath (param "CACHE_DIR"))
+    (subpath (string-append (param "HOME_DIR") "/.gemini"))
+    (subpath (string-append (param "HOME_DIR") "/.npm"))
+    (subpath (string-append (param "HOME_DIR") "/.cache"))
+    (subpath (string-append (param "HOME_DIR") "/.gitconfig"))
+    (literal "/dev/stdout")
+    (literal "/dev/stderr")
+    (literal "/dev/null")
+)
+
+;; deny all inbound network traffic EXCEPT on debugger port
+(deny network-inbound)
+(allow network-inbound (local ip "localhost:9229"))
+
+;; deny all outbound network traffic EXCEPT through proxy on localhost:8877
+;; set `GEMINI_SANDBOX_PROXY_COMMAND=<command>` to run proxy alongside sandbox
+;; proxy must listen on 0.0.0.0:8877 (see scripts/example-proxy.js)
+(deny network-outbound)
+(allow network-outbound (remote tcp "localhost:8877"))
+
+(allow network-bind (local ip "*:*"))
diff --git a/packages/cli/src/utils/sandbox-macos-restrictive-closed.sb b/packages/cli/src/utils/sandbox-macos-restrictive-closed.sb
new file mode 100644
index 00000000..9ce68e9d
--- /dev/null
+++ b/packages/cli/src/utils/sandbox-macos-restrictive-closed.sb
@@ -0,0 +1,87 @@
+(version 1)
+
+;; deny everything by default
+(deny default)
+
+;; allow reading files from anywhere on host
+(allow file-read*)
+
+;; allow exec/fork (children inherit policy)
+(allow process-exec)
+(allow process-fork)
+
+;; allow signals to self, e.g. SIGPIPE on write to closed pipe
+(allow signal (target self))
+
+;; allow read access to specific information about system
+;; from https://source.chromium.org/chromium/chromium/src/+/main:sandbox/policy/mac/common.sb;l=273-319;drc=7b3962fe2e5fc9e2ee58000dc8fbf3429d84d3bd
+(allow sysctl-read
+  (sysctl-name "hw.activecpu")
+  (sysctl-name "hw.busfrequency_compat")
+  (sysctl-name "hw.byteorder")
+  (sysctl-name "hw.cacheconfig")
+  (sysctl-name "hw.cachelinesize_compat")
+  (sysctl-name "hw.cpufamily")
+  (sysctl-name "hw.cpufrequency_compat")
+  (sysctl-name "hw.cputype")
+  (sysctl-name "hw.l1dcachesize_compat")
+  (sysctl-name "hw.l1icachesize_compat")
+  (sysctl-name "hw.l2cachesize_compat")
+  (sysctl-name "hw.l3cachesize_compat")
+  (sysctl-name "hw.logicalcpu_max")
+  (sysctl-name "hw.machine")
+  (sysctl-name "hw.ncpu")
+  (sysctl-name "hw.nperflevels")
+  (sysctl-name "hw.optional.arm.FEAT_BF16")
+  (sysctl-name "hw.optional.arm.FEAT_DotProd")
+  (sysctl-name "hw.optional.arm.FEAT_FCMA")
+  (sysctl-name "hw.optional.arm.FEAT_FHM")
+  (sysctl-name "hw.optional.arm.FEAT_FP16")
+  (sysctl-name "hw.optional.arm.FEAT_I8MM")
+  (sysctl-name "hw.optional.arm.FEAT_JSCVT")
+  (sysctl-name "hw.optional.arm.FEAT_LSE")
+  (sysctl-name "hw.optional.arm.FEAT_RDM")
+  (sysctl-name "hw.optional.arm.FEAT_SHA512")
+  (sysctl-name "hw.optional.armv8_2_sha512")
+  (sysctl-name "hw.packages")
+  (sysctl-name "hw.pagesize_compat")
+  (sysctl-name "hw.physicalcpu_max")
+  (sysctl-name "hw.tbfrequency_compat")
+  (sysctl-name "hw.vectorunit")
+  (sysctl-name "kern.hostname")
+  (sysctl-name "kern.maxfilesperproc")
+  (sysctl-name "kern.osproductversion")
+  (sysctl-name "kern.osrelease")
+  (sysctl-name "kern.ostype")
+  (sysctl-name "kern.osvariant_status")
+  (sysctl-name "kern.osversion")
+  (sysctl-name "kern.secure_kernel")
+  (sysctl-name "kern.usrstack64")
+  (sysctl-name "kern.version")
+  (sysctl-name "sysctl.proc_cputype")
+  (sysctl-name-prefix "hw.perflevel")
+)
+
+;; allow writes to specific paths
+(allow file-write*
+    (subpath (param "TARGET_DIR"))
+    (subpath (param "TMP_DIR"))
+    (subpath (param "CACHE_DIR"))
+    (subpath (string-append (param "HOME_DIR") "/.gemini"))
+    (subpath (string-append (param "HOME_DIR") "/.npm"))
+    (subpath (string-append (param "HOME_DIR") "/.cache"))
+    (subpath (string-append (param "HOME_DIR") "/.gitconfig"))
+    (literal "/dev/stdout")
+    (literal "/dev/stderr")
+    (literal "/dev/null")
+)
+
+;; allow communication with sysmond for process listing (e.g. for pgrep)
+(allow mach-lookup (global-name "com.apple.sysmond"))
+
+;; enable terminal access required by ink
+;; fixes setRawMode EPERM failure (at node:tty:81:24)
+(allow file-ioctl (regex #"^/dev/tty.*"))
+
+;; allow inbound network traffic on debugger port
+(allow network-inbound (local ip "localhost:9229"))
\ No newline at end of file
diff --git a/packages/cli/src/utils/sandbox-macos-strict.sb b/packages/cli/src/utils/sandbox-macos-restrictive-open.sb
similarity index 94%
rename from packages/cli/src/utils/sandbox-macos-strict.sb
rename to packages/cli/src/utils/sandbox-macos-restrictive-open.sb
index 010fee00..e89b8090 100644
--- a/packages/cli/src/utils/sandbox-macos-strict.sb
+++ b/packages/cli/src/utils/sandbox-macos-restrictive-open.sb
@@ -76,15 +76,15 @@
     (literal "/dev/null")
 )
 
-;; allow outbound network connections
-(allow network-outbound)
-
-;; allow inbound network connections to debugging port
-(allow network-inbound (local ip (string-append "*:" "9229")))
-
 ;; allow communication with sysmond for process listing (e.g. for pgrep)
 (allow mach-lookup (global-name "com.apple.sysmond"))
 
 ;; enable terminal access required by ink
 ;; fixes setRawMode EPERM failure (at node:tty:81:24)
 (allow file-ioctl (regex #"^/dev/tty.*"))
+
+;; allow inbound network traffic on debugger port
+(allow network-inbound (local ip "localhost:9229"))
+
+;; allow all outbound network traffic
+(allow network-outbound)
\ No newline at end of file
diff --git a/packages/cli/src/utils/sandbox-macos-restrictive-proxied.sb b/packages/cli/src/utils/sandbox-macos-restrictive-proxied.sb
new file mode 100644
index 00000000..cc4c1e5e
--- /dev/null
+++ b/packages/cli/src/utils/sandbox-macos-restrictive-proxied.sb
@@ -0,0 +1,92 @@
+(version 1)
+
+;; deny everything by default
+(deny default)
+
+;; allow reading files from anywhere on host
+(allow file-read*)
+
+;; allow exec/fork (children inherit policy)
+(allow process-exec)
+(allow process-fork)
+
+;; allow signals to self, e.g. SIGPIPE on write to closed pipe
+(allow signal (target self))
+
+;; allow read access to specific information about system
+;; from https://source.chromium.org/chromium/chromium/src/+/main:sandbox/policy/mac/common.sb;l=273-319;drc=7b3962fe2e5fc9e2ee58000dc8fbf3429d84d3bd
+(allow sysctl-read
+  (sysctl-name "hw.activecpu")
+  (sysctl-name "hw.busfrequency_compat")
+  (sysctl-name "hw.byteorder")
+  (sysctl-name "hw.cacheconfig")
+  (sysctl-name "hw.cachelinesize_compat")
+  (sysctl-name "hw.cpufamily")
+  (sysctl-name "hw.cpufrequency_compat")
+  (sysctl-name "hw.cputype")
+  (sysctl-name "hw.l1dcachesize_compat")
+  (sysctl-name "hw.l1icachesize_compat")
+  (sysctl-name "hw.l2cachesize_compat")
+  (sysctl-name "hw.l3cachesize_compat")
+  (sysctl-name "hw.logicalcpu_max")
+  (sysctl-name "hw.machine")
+  (sysctl-name "hw.ncpu")
+  (sysctl-name "hw.nperflevels")
+  (sysctl-name "hw.optional.arm.FEAT_BF16")
+  (sysctl-name "hw.optional.arm.FEAT_DotProd")
+  (sysctl-name "hw.optional.arm.FEAT_FCMA")
+  (sysctl-name "hw.optional.arm.FEAT_FHM")
+  (sysctl-name "hw.optional.arm.FEAT_FP16")
+  (sysctl-name "hw.optional.arm.FEAT_I8MM")
+  (sysctl-name "hw.optional.arm.FEAT_JSCVT")
+  (sysctl-name "hw.optional.arm.FEAT_LSE")
+  (sysctl-name "hw.optional.arm.FEAT_RDM")
+  (sysctl-name "hw.optional.arm.FEAT_SHA512")
+  (sysctl-name "hw.optional.armv8_2_sha512")
+  (sysctl-name "hw.packages")
+  (sysctl-name "hw.pagesize_compat")
+  (sysctl-name "hw.physicalcpu_max")
+  (sysctl-name "hw.tbfrequency_compat")
+  (sysctl-name "hw.vectorunit")
+  (sysctl-name "kern.hostname")
+  (sysctl-name "kern.maxfilesperproc")
+  (sysctl-name "kern.osproductversion")
+  (sysctl-name "kern.osrelease")
+  (sysctl-name "kern.ostype")
+  (sysctl-name "kern.osvariant_status")
+  (sysctl-name "kern.osversion")
+  (sysctl-name "kern.secure_kernel")
+  (sysctl-name "kern.usrstack64")
+  (sysctl-name "kern.version")
+  (sysctl-name "sysctl.proc_cputype")
+  (sysctl-name-prefix "hw.perflevel")
+)
+
+;; allow writes to specific paths
+(allow file-write*
+    (subpath (param "TARGET_DIR"))
+    (subpath (param "TMP_DIR"))
+    (subpath (param "CACHE_DIR"))
+    (subpath (string-append (param "HOME_DIR") "/.gemini"))
+    (subpath (string-append (param "HOME_DIR") "/.npm"))
+    (subpath (string-append (param "HOME_DIR") "/.cache"))
+    (subpath (string-append (param "HOME_DIR") "/.gitconfig"))
+    (literal "/dev/stdout")
+    (literal "/dev/stderr")
+    (literal "/dev/null")
+)
+
+;; allow communication with sysmond for process listing (e.g. for pgrep)
+(allow mach-lookup (global-name "com.apple.sysmond"))
+
+;; enable terminal access required by ink
+;; fixes setRawMode EPERM failure (at node:tty:81:24)
+(allow file-ioctl (regex #"^/dev/tty.*"))
+
+;; allow inbound network traffic on debugger port
+(allow network-inbound (local ip "localhost:9229"))
+
+;; allow outbound network traffic through proxy on localhost:8877
+;; set `GEMINI_SANDBOX_PROXY_COMMAND=<command>` to run proxy alongside sandbox
+;; proxy must listen on 0.0.0.0:8877 (see scripts/example-proxy.js)
+(allow network-outbound (remote tcp "localhost:8877"))
diff --git a/packages/cli/src/utils/sandbox.ts b/packages/cli/src/utils/sandbox.ts
index c75bd544..b91fd5bf 100644
--- a/packages/cli/src/utils/sandbox.ts
+++ b/packages/cli/src/utils/sandbox.ts
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { execSync, spawnSync, spawn } from 'node:child_process';
+import { execSync, spawn, type ChildProcess } from 'node:child_process';
 import os from 'node:os';
 import path from 'node:path';
 import fs from 'node:fs';
@@ -30,6 +30,16 @@ function getContainerPath(hostPath: string): string {
 }
 
 const LOCAL_DEV_SANDBOX_IMAGE_NAME = 'gemini-cli-sandbox';
+const SANDBOX_NETWORK_NAME = 'gemini-cli-sandbox';
+const SANDBOX_PROXY_NAME = 'gemini-cli-sandbox-proxy';
+const BUILTIN_SEATBELT_PROFILES = [
+  'permissive-open',
+  'permissive-closed',
+  'permissive-proxied',
+  'restrictive-open',
+  'restrictive-closed',
+  'restrictive-proxied',
+];
 
 /**
  * Determines whether the sandbox container should be run with the current user's UID and GID.
@@ -230,14 +240,14 @@ export async function start_sandbox(sandbox: string) {
   if (sandbox === 'sandbox-exec') {
     // disallow BUILD_SANDBOX
     if (process.env.BUILD_SANDBOX) {
-      console.error('ERROR: cannot BUILD_SANDBOX when using MacOC Seatbelt');
+      console.error('ERROR: cannot BUILD_SANDBOX when using MacOS Seatbelt');
       process.exit(1);
     }
-    const profile = (process.env.SEATBELT_PROFILE ??= 'minimal');
+    const profile = (process.env.SEATBELT_PROFILE ??= 'permissive-open');
     let profileFile = new URL(`sandbox-macos-${profile}.sb`, import.meta.url)
       .pathname;
-    // if profile is anything other than 'minimal' or 'strict', then look for the profile file under the project settings directory
-    if (profile !== 'minimal' && profile !== 'strict') {
+    // if profile name is not recognized, then look for file under project settings directory
+    if (!BUILTIN_SEATBELT_PROFILES.includes(profile)) {
       profileFile = path.join(
         SETTINGS_DIRECTORY_NAME,
         `sandbox-macos-${profile}.sb`,
@@ -251,10 +261,6 @@ export async function start_sandbox(sandbox: string) {
     }
     console.error(`using macos seatbelt (profile: ${profile}) ...`);
     // if DEBUG is set, convert to --inspect-brk in NODE_OPTIONS
-    if (process.env.DEBUG) {
-      process.env.NODE_OPTIONS ??= '';
-      process.env.NODE_OPTIONS += ` --inspect-brk`;
-    }
     const args = [
       '-D',
       `TARGET_DIR=${fs.realpathSync(process.cwd())}`,
@@ -270,11 +276,67 @@ export async function start_sandbox(sandbox: string) {
       '-c',
       [
         `SANDBOX=sandbox-exec`,
-        `NODE_OPTIONS="${process.env.NODE_OPTIONS}"`,
+        `NODE_OPTIONS="${process.env.DEBUG ? `--inspect-brk` : ''}"`,
         ...process.argv.map((arg) => quote([arg])),
       ].join(' '),
     ];
-    spawnSync(sandbox, args, { stdio: 'inherit' });
+    // start and set up proxy if GEMINI_SANDBOX_PROXY_COMMAND is set
+    const proxyCommand = process.env.GEMINI_SANDBOX_PROXY_COMMAND;
+    let proxyProcess: ChildProcess | undefined;
+    const sandboxEnv = { ...process.env };
+    if (proxyCommand) {
+      const proxy =
+        process.env.HTTPS_PROXY ||
+        process.env.https_proxy ||
+        process.env.HTTP_PROXY ||
+        process.env.http_proxy ||
+        'http://localhost:8877';
+      sandboxEnv['HTTPS_PROXY'] = proxy;
+      sandboxEnv['https_proxy'] = proxy; // lower-case can be required, e.g. for curl
+      sandboxEnv['HTTP_PROXY'] = proxy;
+      sandboxEnv['http_proxy'] = proxy;
+      const noProxy = process.env.NO_PROXY || process.env.no_proxy;
+      if (noProxy) {
+        sandboxEnv['NO_PROXY'] = noProxy;
+        sandboxEnv['no_proxy'] = noProxy;
+      }
+      proxyProcess = spawn(proxyCommand, {
+        stdio: ['ignore', 'pipe', 'pipe'],
+        shell: true,
+        detached: true,
+      });
+      // commented out as it disrupts ink rendering
+      // proxyProcess.stdout?.on('data', (data) => {
+      //   console.info(data.toString());
+      // });
+      proxyProcess.stderr?.on('data', (data) => {
+        console.error(data.toString());
+      });
+      console.log('waiting for proxy to start ...');
+      execSync(`until lsof -i :8877 | grep -q "LISTEN"; do sleep 0.1; done`);
+    }
+    try {
+      // spawn child and let it inherit stdio
+      const child = spawn(sandbox, args, {
+        stdio: 'inherit',
+        env: sandboxEnv,
+      });
+      if (proxyProcess) {
+        proxyProcess.on('close', (code, signal) => {
+          console.error(
+            `ERROR: proxy command '${proxyCommand}' exited with code ${code}, signal ${signal}`,
+          );
+          if (child.pid) {
+            process.kill(-child.pid, 'SIGTERM');
+          }
+        });
+      }
+      await new Promise((resolve) => child.on('close', resolve));
+    } finally {
+      if (proxyProcess?.pid) {
+        process.kill(-proxyProcess.pid, 'SIGTERM');
+      }
+    }
     return;
   }
 
@@ -408,6 +470,45 @@ export async function start_sandbox(sandbox: string) {
     args.push(`--publish`, `${debugPort}:${debugPort}`);
   }
 
+  // copy proxy environment variables, replacing localhost with SANDBOX_PROXY_NAME
+  // copy as both upper-case and lower-case as is required by some utilities
+  // GEMINI_SANDBOX_PROXY_COMMAND implies HTTPS_PROXY unless HTTP_PROXY is set
+  const proxyCommand = process.env.GEMINI_SANDBOX_PROXY_COMMAND;
+  let proxy =
+    process.env.HTTPS_PROXY ||
+    process.env.https_proxy ||
+    process.env.HTTP_PROXY ||
+    process.env.http_proxy ||
+    'http://localhost:8877';
+  proxy = proxy.replace('localhost', SANDBOX_PROXY_NAME);
+  if (proxy) {
+    args.push('--env', `HTTPS_PROXY=${proxy}`);
+    args.push('--env', `https_proxy=${proxy}`); // lower-case can be required, e.g. for curl
+    args.push('--env', `HTTP_PROXY=${proxy}`);
+    args.push('--env', `http_proxy=${proxy}`);
+  }
+  const noProxy = process.env.NO_PROXY || process.env.no_proxy;
+  if (noProxy) {
+    args.push('--env', `NO_PROXY=${noProxy}`);
+    args.push('--env', `no_proxy=${noProxy}`);
+  }
+
+  // if using proxy, switch to internal networking through proxy
+  if (proxy) {
+    execSync(
+      `${sandbox} network exists ${SANDBOX_NETWORK_NAME} || ${sandbox} network create --internal ${SANDBOX_NETWORK_NAME}`,
+    );
+    args.push('--network', SANDBOX_NETWORK_NAME);
+    // if proxy command is set, create a separate network w/ host access (i.e. non-internal)
+    // we will run proxy in its own container connected to both host network and internal network
+    // this allows proxy to work even on rootless podman on macos with host<->vm<->container isolation
+    if (proxyCommand) {
+      execSync(
+        `${sandbox} network exists ${SANDBOX_PROXY_NAME} || ${sandbox} network create ${SANDBOX_PROXY_NAME}`,
+      );
+    }
+  }
+
   // name container after image, plus numeric suffix to avoid conflicts
   const imageName = parseImageName(image);
   let index = 0;
@@ -510,28 +611,52 @@ export async function start_sandbox(sandbox: string) {
   // push container entrypoint (including args)
   args.push(...entrypoint(workdir));
 
-  // spawn child and let it inherit stdio
-  const child = spawn(sandbox, args, {
-    stdio: 'inherit',
-    detached: os.platform() !== 'win32',
-  });
-
-  child.on('error', (err) => {
-    console.error('Sandbox process error:', err);
-  });
-
-  // uncomment this line (and comment the await on following line) to let parent exit
-  // child.unref();
-  await new Promise<void>((resolve) => {
-    child.on('close', (code, signal) => {
-      if (code !== 0) {
-        console.log(
-          `Sandbox process exited with code: ${code}, signal: ${signal}`,
-        );
-      }
-      resolve();
+  // start and set up proxy if GEMINI_SANDBOX_PROXY_COMMAND is set
+  let proxyProcess: ChildProcess | undefined;
+  if (proxyCommand) {
+    // run proxyCommand in its own container
+    const proxyContainerCommand = `${sandbox} run --rm --init --name ${SANDBOX_PROXY_NAME} --network ${SANDBOX_PROXY_NAME} --network ${SANDBOX_NETWORK_NAME} -p 8877:8877 -v ${process.cwd()}:${workdir} --workdir ${workdir} ${image} ${proxyCommand}`;
+    proxyProcess = spawn(proxyContainerCommand, {
+      stdio: ['ignore', 'pipe', 'pipe'],
+      shell: true,
+      detached: true,
     });
-  });
+    // commented out as it disrupts ink rendering
+    // proxyProcess.stdout?.on('data', (data) => {
+    //   console.info(data.toString());
+    // });
+    proxyProcess.stderr?.on('data', (data) => {
+      console.error(data.toString().trim());
+    });
+    console.log('waiting for proxy to start ...');
+    execSync(`until lsof -i :8877 | grep -q "LISTEN"; do sleep 0.1; done`);
+  }
+
+  try {
+    // spawn child and let it inherit stdio
+    const child = spawn(sandbox, args, {
+      stdio: 'inherit',
+    });
+
+    child.on('error', (err) => {
+      console.error('Sandbox process error:', err);
+    });
+
+    await new Promise<void>((resolve) => {
+      child.on('close', (code, signal) => {
+        if (code !== 0) {
+          console.log(
+            `Sandbox process exited with code: ${code}, signal: ${signal}`,
+          );
+        }
+        resolve();
+      });
+    });
+  } finally {
+    if (proxyProcess?.pid) {
+      process.kill(-proxyProcess.pid, 'SIGTERM');
+    }
+  }
 }
 
 // Helper functions to ensure sandbox image is present
diff --git a/packages/core/package.json b/packages/core/package.json
index 344f3a5a..033fbddc 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -34,7 +34,8 @@
     "fast-glob": "^3.3.3",
     "ignore": "^7.0.0",
     "shell-quote": "^1.8.2",
-    "strip-ansi": "^7.1.0"
+    "strip-ansi": "^7.1.0",
+    "undici": "^7.10.0"
   },
   "devDependencies": {
     "@types/diff": "^7.0.2",
diff --git a/packages/core/src/core/client.ts b/packages/core/src/core/client.ts
index 1b953d30..3046116e 100644
--- a/packages/core/src/core/client.ts
+++ b/packages/core/src/core/client.ts
@@ -38,6 +38,18 @@ import {
   createContentGenerator,
 } from './contentGenerator.js';
 
+import { ProxyAgent, setGlobalDispatcher } from 'undici';
+
+const proxy =
+  process.env.HTTPS_PROXY ||
+  process.env.https_proxy ||
+  process.env.HTTP_PROXY ||
+  process.env.http_proxy;
+
+if (proxy) {
+  setGlobalDispatcher(new ProxyAgent(proxy));
+}
+
 export class GeminiClient {
   private chat: Promise<GeminiChat>;
   private contentGenerator: ContentGenerator;
diff --git a/scripts/build_sandbox.js b/scripts/build_sandbox.js
index bfcf1bf9..89e186fa 100644
--- a/scripts/build_sandbox.js
+++ b/scripts/build_sandbox.js
@@ -111,7 +111,7 @@ function buildImage(imageName, dockerfile) {
 
   execSync(
     `${buildCommand} ${process.env.BUILD_SANDBOX_FLAGS || ''} -f "${dockerfile}" -t "${imageName}" .`,
-    { stdio: buildStdout },
+    { stdio: buildStdout, shell: '/bin/bash' },
   );
   console.log(`built ${imageName}`);
 }
diff --git a/scripts/example-proxy.js b/scripts/example-proxy.js
new file mode 100755
index 00000000..284a2eed
--- /dev/null
+++ b/scripts/example-proxy.js
@@ -0,0 +1,74 @@
+#!/usr/bin/env node
+
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// Example proxy server that listens on 0.0.0.0:8877 and only allows HTTPS connections to example.com.
+// Set `GEMINI_SANDBOX_PROXY_COMMAND=scripts/example-proxy.js` to run proxy alongside sandbox
+// Test via `curl https://example.com` inside sandbox (in shell mode or via shell tool)
+
+import http from 'http';
+import net from 'net';
+import { URL } from 'url';
+import console from 'console';
+
+const PROXY_PORT = 8877;
+const ALLOWED_DOMAINS = ['example.com', 'googleapis.com'];
+const ALLOWED_PORT = '443';
+
+const server = http.createServer((req, res) => {
+  // Deny all requests other than CONNECT for HTTPS
+  console.log(
+    `[PROXY] Denying non-CONNECT request for: ${req.method} ${req.url}`,
+  );
+  res.writeHead(405, { 'Content-Type': 'text/plain' });
+  res.end('Method Not Allowed');
+});
+
+server.on('connect', (req, clientSocket, head) => {
+  // req.url will be in the format "hostname:port" for a CONNECT request.
+  const { port, hostname } = new URL(`http://${req.url}`);
+
+  console.log(`[PROXY] Intercepted CONNECT request for: ${hostname}:${port}`);
+
+  if (
+    ALLOWED_DOMAINS.some(
+      (domain) => hostname == domain || hostname.endsWith(`.${domain}`),
+    ) &&
+    port === ALLOWED_PORT
+  ) {
+    console.log(`[PROXY] Allowing connection to ${hostname}:${port}`);
+
+    // Establish a TCP connection to the original destination.
+    const serverSocket = net.connect(port, hostname, () => {
+      clientSocket.write('HTTP/1.1 200 Connection Established\r\n\r\n');
+      // Create a tunnel by piping data between the client and the destination server.
+      serverSocket.write(head);
+      serverSocket.pipe(clientSocket);
+      clientSocket.pipe(serverSocket);
+    });
+
+    serverSocket.on('error', (err) => {
+      console.error(`[PROXY] Error connecting to destination: ${err.message}`);
+      clientSocket.end(`HTTP/1.1 502 Bad Gateway\r\n\r\n`);
+    });
+  } else {
+    console.log(`[PROXY] Denying connection to ${hostname}:${port}`);
+    clientSocket.end('HTTP/1.1 403 Forbidden\r\n\r\n');
+  }
+
+  clientSocket.on('error', (err) => {
+    // This can happen if the client hangs up.
+    console.error(`[PROXY] Client socket error: ${err.message}`);
+  });
+});
+
+server.listen(PROXY_PORT, '0.0.0.0', () => {
+  console.log(`[PROXY] Proxy listening on 0.0.0.0:${PROXY_PORT}`);
+  console.log(
+    `[PROXY] Allowing HTTPS connections to domains: ${ALLOWED_DOMAINS.join(', ')}`,
+  );
+});
diff --git a/scripts/start.js b/scripts/start.js
index f9f85c8e..d38e00f6 100644
--- a/scripts/start.js
+++ b/scripts/start.js
@@ -33,11 +33,12 @@ execSync('node ./scripts/check-build-status.js', {
 // inside sandbox SANDBOX should be set and sandbox_command.js should fail
 const nodeArgs = [];
 try {
-  execSync('node scripts/sandbox_command.js -q', {
-    stdio: 'inherit',
+  const sandboxCommand = execSync('node scripts/sandbox_command.js', {
     cwd: root,
-  });
-  if (process.env.DEBUG) {
+  })
+    .toString()
+    .trim();
+  if (process.env.DEBUG && !sandboxCommand) {
     if (process.env.SANDBOX) {
       const port = process.env.DEBUG_PORT || '9229';
       nodeArgs.push(`--inspect-brk=0.0.0.0:${port}`);