diff --git a/cloud/apps/sandbox-control/migrations/0032_egress_user_hosts.sql b/cloud/apps/sandbox-control/migrations/0032_egress_user_hosts.sql
new file mode 100644
index 00000000000..89cc3a8702e
--- /dev/null
+++ b/cloud/apps/sandbox-control/migrations/0032_egress_user_hosts.sql
@@ -0,0 +1,4 @@
+-- Hosts the workspace's own agent tools need (remote MCP servers synced from the desktop), added to
+-- the egress allowlist on every boot (comma list). Set by PUT /v1/sandboxes/:id/egress/hosts; unlike
+-- egress_allow_hosts it is not recomputed from secrets.
+ALTER TABLE sandboxes ADD COLUMN egress_user_hosts TEXT;
diff --git a/cloud/apps/sandbox-control/src/egress-hosts.ts b/cloud/apps/sandbox-control/src/egress-hosts.ts
new file mode 100644
index 00000000000..7fb5201a181
--- /dev/null
+++ b/cloud/apps/sandbox-control/src/egress-hosts.ts
@@ -0,0 +1,55 @@
+// Hosts a workspace's own agent tools need beyond the default allowlist — today the remote MCP
+// servers the desktop syncs into the sandbox (MCP config sync). The desktop declares them with
+// PUT /v1/sandboxes/:id/egress/hosts {hosts}; they persist on the row (every boot re-applies them)
+// and a running sandbox's policy is rewritten at once. Public hostnames only: no wildcards, IPs,
+// localhost or private suffixes, so the fail-closed allowlist can't be turned into "open".
+import { z } from 'zod'
+import { egressPolicy, refreshGitCredentials, type LifecycleDeps } from './lifecycle'
+import { transition, type SandboxRow } from './store'
+
+export const MAX_USER_HOSTS = 32
+const HOST = /^([a-z0-9-]+\.)+[a-z]{2,63}$/
+const PRIVATE_SUFFIXES = ['.local', '.localhost', '.internal', '.lan', '.home', '.corp', '.intranet']
+
+export const EgressHostsSchema = z
+  .object({ hosts: z.array(z.string().min(1).max(253)).max(MAX_USER_HOSTS) })
+  .strict()
+
+/** Normalized, deduplicated, sorted; null when any entry is not an acceptable public hostname. */
+export function normalizeUserHosts(hosts: readonly string[]): string[] | null {
+  const out = new Set<string>()
+  for (const raw of hosts) {
+    const host = raw.trim().toLowerCase().replace(/\.$/, '')
+    if (!HOST.test(host) || PRIVATE_SUFFIXES.some((suffix) => host.endsWith(suffix))) {
+      return null
+    }
+    out.add(host)
+  }
+  return [...out].sort()
+}
+
+export function egressUserHosts(row: Pick<SandboxRow, 'egress_user_hosts'>): string[] {
+  return (row.egress_user_hosts ?? '').split(',').filter(Boolean)
+}
+
+/** Records the hosts and, for a running sandbox, rewrites its policy now. */
+export async function setEgressUserHosts(deps: LifecycleDeps, row: SandboxRow, hosts: string[]): Promise<SandboxRow | null> {
+  const value = hosts.join(',') || null
+  if (value === row.egress_user_hosts) {
+    return row
+  }
+  const next = await transition(deps.db, row, { egress_user_hosts: value }, deps.now())
+  if (!next) {
+    return null
+  }
+  if (next.status === 'running' && next.session_id) {
+    // A policy write replaces the whole policy, so the git route is re-minted alongside.
+    const git = await refreshGitCredentials(deps, next, next.session_id)
+    if (!git) {
+      await deps.provider.updateNetworkPolicy(next.session_id, egressPolicy(deps, next))
+    }
+  }
+  // Counts only; hostnames are not secrets but stay out of logs anyway (they can name private tools).
+  console.log(JSON.stringify({ event: 'egress_user_hosts_set', sandboxId: row.id, count: hosts.length }))
+  return next
+}
diff --git a/cloud/apps/sandbox-control/src/index.ts b/cloud/apps/sandbox-control/src/index.ts
index 91dcaf9e9a6..165de0ad033 100644
--- a/cloud/apps/sandbox-control/src/index.ts
+++ b/cloud/apps/sandbox-control/src/index.ts
@@ -85,6 +85,7 @@ import { reconcile } from './reconcile'
 import { egressSecretHosts, secretPlaceholder } from './secret-egress'
 import { SecretError, handleSecretsRoute, keyringFor, type SecretChange } from './secrets'
 import { refreshAfterSecretChange, refreshSandboxEnv } from './env-refresh'
+import { EgressHostsSchema, egressUserHosts, normalizeUserHosts, setEgressUserHosts } from './egress-hosts'
 import { cachedProviderEnv } from './session-env'
 import { credentialTargets } from './provider-env'
 import type { Keyring } from './secrets-crypto'
@@ -972,7 +973,7 @@ export async function handleRequest(request: Request, env: Env, deps: Deps = {})
       return await workspaceRoute(request, url, env, deps, caller)
     }
     const match =
-      /^\/v1\/sandboxes(?:\/([A-Za-z0-9_]+)(?:\/(suspend|resume|lease|rollover|wake|restart|status|archive|unarchive|env\/refresh|ssh-keys|desktop))?)?$/.exec(
+      /^\/v1\/sandboxes(?:\/([A-Za-z0-9_]+)(?:\/(suspend|resume|lease|rollover|wake|restart|status|archive|unarchive|env\/refresh|egress\/hosts|ssh-keys|desktop))?)?$/.exec(
         url.pathname
       )
     if (!match) {
@@ -1073,6 +1074,20 @@ export async function handleRequest(request: Request, env: Env, deps: Deps = {})
       }
       case 'POST env/refresh':
         return json({ applied: await refreshSandboxEnv(life, row) })
+      case 'GET egress/hosts':
+        return json({ hosts: egressUserHosts(row) })
+      case 'PUT egress/hosts': {
+        const body = EgressHostsSchema.safeParse(await readJson(request))
+        const hosts = body.success ? normalizeUserHosts(body.data.hosts) : null
+        if (!hosts) {
+          return fail('invalid_request', 400, 'invalid_host')
+        }
+        const next = await setEgressUserHosts(life, row, hosts)
+        if (!next) {
+          return fail('conflict', 409, 'concurrent_transition')
+        }
+        return json({ hosts: egressUserHosts(next) })
+      }
       case 'POST desktop': {
         // Runs only the image's fixed entry point; the desktop listens on the VM's loopback and is
         // reached through the paired runtime's port forward, never a public route.
diff --git a/cloud/apps/sandbox-control/src/lifecycle.ts b/cloud/apps/sandbox-control/src/lifecycle.ts
index 2749dbe6618..33821170262 100644
--- a/cloud/apps/sandbox-control/src/lifecycle.ts
+++ b/cloud/apps/sandbox-control/src/lifecycle.ts
@@ -300,7 +300,7 @@ async function boot(
   // Nothing in the VM uses git or model keys before orcad answers and the desktop attaches.
   const needsPolicy =
     !options.policyApplied &&
-    (git || routed.egress_secret_hosts || row.egress_secret_hosts || routed.egress_allow_hosts || row.egress_allow_hosts)
+    (git || routed.egress_secret_hosts || row.egress_secret_hosts || routed.egress_allow_hosts || row.egress_allow_hosts || row.egress_user_hosts)
   // Members revoked while the VM slept must be gone before orcad accepts its first sign-in.
   await applyQueuedRevokes(deps.db, deps.provider, row.id, state.session.id, deps.now())
   const [, connection] = await Promise.all([
diff --git a/cloud/apps/sandbox-control/src/session-env.ts b/cloud/apps/sandbox-control/src/session-env.ts
index f704b4941b4..e039f8cd2b1 100644
--- a/cloud/apps/sandbox-control/src/session-env.ts
+++ b/cloud/apps/sandbox-control/src/session-env.ts
@@ -84,6 +84,7 @@ export async function sessionSecretEnv(
   return { env: swapped.env, egressSecretHosts: encodeEgressSecretHosts(swapped.targets), egressAllowHosts }
 }
 
-export function egressAllowHosts(row: Pick<SandboxRow, 'egress_allow_hosts'>): string[] {
-  return (row.egress_allow_hosts ?? '').split(',').filter(Boolean)
+/** Provider hosts from the session's secrets plus the workspace's declared tool hosts (MCP). */
+export function egressAllowHosts(row: Pick<SandboxRow, 'egress_allow_hosts'> & Partial<Pick<SandboxRow, 'egress_user_hosts'>>): string[] {
+  return [...(row.egress_allow_hosts ?? '').split(','), ...(row.egress_user_hosts ?? '').split(',')].filter(Boolean)
 }
diff --git a/cloud/apps/sandbox-control/src/store.ts b/cloud/apps/sandbox-control/src/store.ts
index e95ea8997d2..99d08aeda19 100644
--- a/cloud/apps/sandbox-control/src/store.ts
+++ b/cloud/apps/sandbox-control/src/store.ts
@@ -40,6 +40,8 @@ export type SandboxRow = {
   egress_secret_hosts: string | null
   /** Comma list of custom model-provider hosts added to this session's egress allowlist. */
   egress_allow_hosts: string | null
+  /** Comma list of hosts the workspace's own tools need (synced remote MCP servers); set by the desktop. */
+  egress_user_hosts: string | null
   retention_warned_at: number | null
   /** Environment build this sandbox first booted from (null: the golden image). Never changes. */
   environment_id: string | null
@@ -178,7 +180,7 @@ type Patch = Partial<Omit<SandboxRow, 'id' | 'account_id' | 'generation' | 'crea
 const PATCHABLE = new Set<string>([
   'status', 'session_id', 'session_started_at', 'session_deadline_at', 'lease_expires_at',
   'usage_settled_at', 'last_error', 'destroyed_at', 'github_token_expires_at',
-  'egress_secret_hosts', 'egress_allow_hosts', 'repo_url', 'retention_warned_at', 'orcad_endpoint', 'ready_at',
+  'egress_secret_hosts', 'egress_allow_hosts', 'egress_user_hosts', 'repo_url', 'retention_warned_at', 'orcad_endpoint', 'ready_at',
   'archived_at', 'archive_expires_at'
 ])
 
diff --git a/cloud/apps/sandbox-control/test/agent-providers.test.ts b/cloud/apps/sandbox-control/test/agent-providers.test.ts
index 32ef3849816..f564e04c6b1 100644
--- a/cloud/apps/sandbox-control/test/agent-providers.test.ts
+++ b/cloud/apps/sandbox-control/test/agent-providers.test.ts
@@ -327,3 +327,27 @@ describe('staged egress placeholder rollout', () => {
     expect(row!.egress_secret_hosts).toBe('ANTHROPIC_AUTH_TOKEN@llm.example.com')
   })
 })
+
+describe('workspace tool hosts (synced remote MCP servers)', () => {
+  it('opens declared hosts on the running sandbox now and on every later boot; refuses wildcards and private names', async () => {
+    const { h, as } = await setup()
+    const mia = await as('mia')
+    const created = await h.call('POST', '/v1/sandboxes', { body: { workspaceId: 'ws-1', machineSize: 'standard' }, bearer: mia })
+    const id: string = created.body.sandbox.id
+    const box = () => [...h.vercel.boxes.values()][0]!
+    expect(box().policy.allow['mcp.linear.app']).toBeUndefined()
+    const put = await h.call('PUT', `/v1/sandboxes/${id}/egress/hosts`, { bearer: mia, body: { hosts: ['MCP.linear.app', 'mcp.notion.com.', 'mcp.linear.app'] } })
+    expect(put.body).toEqual({ hosts: ['mcp.linear.app', 'mcp.notion.com'] })
+    expect(box().policy.allow['mcp.linear.app']).toEqual([])
+    expect(box().policy.allow['*']).toBeUndefined()
+    for (const bad of ['*', '*.example.com', '10.0.0.1', 'localhost', 'box.internal', 'http://x.example.com']) {
+      expect((await h.call('PUT', `/v1/sandboxes/${id}/egress/hosts`, { bearer: mia, body: { hosts: [bad] } })).status).toBe(400)
+    }
+    expect((await h.call('PUT', `/v1/sandboxes/${id}/egress/hosts`, { bearer: await as('bob'), body: { hosts: ['x.example.com'] } })).status).toBe(404)
+    // Sleep and wake: the hosts come back with the new session's policy.
+    await h.call('POST', `/v1/sandboxes/${id}/suspend`, { bearer: mia })
+    await h.call('POST', `/v1/sandboxes/${id}/resume`, { bearer: mia })
+    expect(box().policy.allow['mcp.notion.com']).toEqual([])
+    expect((await h.call('GET', `/v1/sandboxes/${id}/egress/hosts`, { bearer: mia })).body).toEqual({ hosts: ['mcp.linear.app', 'mcp.notion.com'] })
+  })
+})