A sandbox can isolate a process while still letting generated code send data to the public internet. If restricted outbound networking is part of the requirement, compare the network policy itself: its default, enforcement scope, supported destinations and exceptions.

E2B, Daytona, Modal, Blaxel and Northflank are credible directions to investigate, but their controls and operating models are not identical. This guide is for teams selecting execution infrastructure for generated code. It is not a penetration test or a guarantee against exfiltration.

What qualifies for this comparison

We looked for current official evidence of outbound restrictions, rather than assuming that “sandbox” implies deny-by-default networking. We distinguish SDK documentation from vendor descriptions and identify beta, tier and deployment boundaries. Browser-only automation environments are not automatically interchangeable with general code sandboxes.

Platform	Documented control	Default or scope that matters	Evaluation caution
E2B	Disable internet or combine outbound allow/deny lists	Outbound internet enabled by default	Domain filtering has protocol and shared-endpoint limits
Daytona	Block-all, CIDR or domain settings	Organisation tier controls what can be overridden	Sandbox modes are mutually exclusive in current docs
Modal	Block network, CIDR and domain controls	Public outbound access allowed by default	Domain control is Beta; DNS and TLS/SNI limits matter
Blaxel	Vendor-described network-layer workload allowlists	Vendor says workloads start closed	Obtain the exact contract and operational evidence
Northflank	Ingress/egress network policies	Documented application policy scope is BYOC clusters	Validate workload targeting; no rules means allowed traffic

E2B: deny the rest, not just list a destination

E2B’s current network documentation describes an internet switch and fine-grained allow/deny lists. For domain restriction, it requires denying other traffic; an allowed hostname alone is not an all-purpose block policy.

Its documented limits matter: domain filtering concerns HTTP/TLS on particular ports, DNS has a necessary exception, and shared endpoints can weaken a hostname boundary. The docs also warn that a blocked connection can appear open before application traffic is evaluated. Validate an actual response and destination-side evidence, not just a successful socket call.

Daytona: match the policy to the account tier

Daytona’s network-limit documentation distinguishes organisation-tier restrictions from sandbox settings. Lower tiers cannot override the organisation policy; higher tiers allow custom sandbox restrictions and otherwise have wider default access.

The current documented block-all, CIDR and domain modes are mutually exclusive. Essential services are not a universal bypass of a custom higher-tier sandbox restriction. This makes the account tier and precise configuration part of the purchase decision. Do not rely on a cached example or an alternative documentation hostname when the current canonical docs describe a different API.

Modal: read the domain-filter caveats

Modal’s sandbox-networking guide documents full blocking, CIDR restrictions and a Beta TLS-domain allowlist. It distinguishes the network policy from the isolation runtime and explains DNS and shared-TLS-endpoint limitations.

This is a strong evaluation route when the team needs to reason explicitly about IP ranges, HTTPS names and sandbox runtime choices. Do not describe the Beta domain control as URL-path filtering or a general content inspection service. Ask how any sidecar proxy changes the enforcement boundary before copying a policy between configurations.

Blaxel: verify the vendor-described closed starting point

Blaxel’s networking page says outbound allowlists are enforced at the network layer and workloads start closed. That is directly relevant to this buying intent, but it remains a vendor description, not an independently verified security result.

Require a demonstration with your workload, requested destinations and credential handling. Establish who can change an allowlist and what appears in denied-traffic logs. Also confirm that the deployed product and purchased plan implement the described policy; a platform overview should not replace a specific operating agreement.

Northflank: a broader runtime with explicit policy targeting

Northflank’s network-policy documentation describes controls for workloads and projects on BYOC clusters, including deny-all and external IP/CIDR/FQDN destinations. It also states that traffic is allowed in a direction when no rules are defined there. Its sandbox-networking article explains the broader agent-runtime direction.

Investigate this when managing the execution environment within a broader cloud/network arrangement is part of the requirement. Verify the exact sandbox deployment and policy entitlement: application-level BYOC documentation is not proof that every hosted service inherits the same controls. Incorrect workload tags can leave the intended policy unapplied.

Test the boundary, not the marketing label

Use an isolated evaluation with synthetic data and endpoints you control. First permit one destination and deny another. Repeat by hostname and IP, follow an approved endpoint’s redirect, and test the ports and protocols the application actually needs. Inspect destination-side logs and the platform’s denied-traffic evidence.

Then check what happens during dependency installation and image preparation. A restricted execution phase does not prove that every earlier build or fetch phase used the same rule. The point is to map each phase, not to claim that these platforms share a bypass.

Finally, separate outbound controls from inbound exposure and secret access. A narrowly allowed service can still receive data that the workload is permitted to send. Do not put an unrestricted credential into generated code merely because a network allowlist exists.

Cost and choice

Compare runtime, idle/suspended behaviour, storage, network egress, required tiers, BYOC operations and observability access. Shortlist the platforms whose documented boundary matches your protocols and deployment; then test the configuration before production use.

Use agent authentication and scoped permissions alongside network controls. For the underlying network concepts, see Docker networking: process isolation, inbound ports and outbound reachability are separate questions even when a managed platform hides much of the plumbing.

Official sources checked 20 October 2026. No intrusion test, data-loss-prevention certification or paid inclusion is claimed.