Head to head · Code sandboxes · October 2026 research run

Celesto (formerly SmolVM) vs Deno Sandbox

Celesto (formerly SmolVM) scores 68 (B) on agent readiness against Deno Sandbox's 49.5 (D), and leads in 6 of 7 scored categories. Deno Sandbox leads on security & auth. Both do code sandboxes.

Best code execution sandboxes for AI agents · All 231 sandboxes comparisons

Which one, for what

Celesto (formerly SmolVM) B

Best for Local microVM sandboxes for agent code, browsers and desktops on Linux and macOS, with a path to a hosted cloud.

Ahead on

  • Reliability, 66 against 43
  • Schema & documentation, 85 against 66
  • Agent ergonomics, 69 against 60
  • Payments & pricing, 60 against 20
  • Maintenance & community, 81 against 45

Also in its favour

  • No key needed to call it
  • Free to start without a card
  • Open source

Watch for

Version 0.1.13 and declared pre-1.0 in SECURITY.md, with the TypeScript SDK an alpha installed from a GitHub tarball

Deno Sandbox D

Best for Short runs of untrusted or generated code that need outside API keys kept out of reach, for teams already on Deno Deploy, until Deploy closes six months after 9 October 2026.

Ahead on

  • Security & auth, 58 against 52

Watch for

Deno Deploy, which runs Sandbox, shuts down six months after the 9 October 2026 announcement, and Deno is moving its development to Cloudflare

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Payments & pricing Celesto (formerly SmolVM) +40

Celesto (formerly SmolVM) 60

Read with the self-hosted rule, scoring the hosted option for the price lines. No x402, MPP or L402 (0 of 40). Celesto Cloud publishes hourly prices for six sizes without a login (20). A one-time $5 Micro credit needs no card, and the local SDK is free (20). The graded local SDK installs from PyPI and runs with no account, so an agent needs no signup (20). Cloud use needs a browser signup and a card top-up. Total 60.

Deno Sandbox 20

No x402, MPP or L402 (0). Unit prices are public without a login, $0.10 a CPU-hour, $0.025 a GiB-hour and $0.20 a GiB-month (20). The Free plan does not include sandboxes, and no trial was found (0). A person signs up at console.deno.com in a browser and creates the token (0). 0+20+0+0 = 20.

Maintenance & community Celesto (formerly SmolVM) +36

Celesto (formerly SmolVM) 81

0.1.13 on PyPI on 5 November 2026, tagged 6 November (30). 22 PyPI releases in the 90 days to 6 November (20). Most open issues are filed by maintainers. Outside reports such as the thread-safety issue got replies, and several recent ones have none yet; pull-request reply times were not read (15 of 25). The Python SDK is current, the TypeScript SDK is an alpha not published to npm (8 of 15). uv and Cargo lock files, CodeQL and publish workflows, with run results unread (8 of 10). Total 81.

Deno Sandbox 45

Deno 2.9.7 (16 September 2026, 49 days ago) includes a fix to how the deno sandbox command passes its arguments, the newest release touching the product. deno-sandbox 0.16.0 shipped on 22 July 2026, and @deno/sandbox 0.13.2 on 16 March per the 8 October check (20). One release in the 90 days from 6 August (0). The Deploy changelog stops at 12 March 2026. Support is by Discord, and by email on paid plans. The Python repository showed one open issue or pull request on 8 October (7). Official JavaScript and Python SDKs, the JavaScript one unchanged since March (12). The Python repository runs formatting, lint, type checks and offline tests in CI. The JavaScript SDK's source repository is not public (6). 20+0+7+12+6 = 45.

Reliability Celesto (formerly SmolVM) +23

Celesto (formerly SmolVM) 66

Read with the local-software lines, because the graded surface runs on the owner's machine. Installs from PyPI as celesto with Python 3.11 or newer on Linux and macOS stated, plus an install script (20). The repository has pytest, e2e, lint, TypeScript and smoke-test workflows and 38 test packages, but GitHub's API answered with a rate limit, so no run result was read (15 of 25, unchecked). 22 open issues and pull requests against about 188 commits in 90 days. The open bugs include a snapshot restore that can lose a VM's disk if interrupted and a thread-safety issue with five replies (18 of 25). A dated changelog with Security, Fixed, Added and Removed sections, and the rename to Celesto marked as a breaking release, though versions stay below 1.0 (13 of 15). Pre-1.0 per SECURITY.md (0). Total 66.

Deno Sandbox 43

Hosted lines. denostatus.com runs on Instatus with history, but has no component for sandboxes (15 of 20). The 90 days from 6 August show one incident, request failures in ord on 7 September 2026, one region, so minor (20). Concurrency and resource limits are published, though the docs (5 per organisation) and the pricing table (3 per region on Pro) differ, and no API request limits were found (8, a partial value kept). No 429 or retry guidance and no idempotency keys found (0). The pricing table lists a 99.95 per cent reliability SLA for Enterprise, with no SLA document found (0). Beta, pre-release per the docs (0). 15+20+8+0+0+0 = 43.

Schema & documentation Celesto (formerly SmolVM) +19

Celesto (formerly SmolVM) 85

Read as an SDK and CLI. The repository ships an OpenAPI document for the local server (24 operations) and the cloud API (171 operations), from which the TypeScript client is generated (25). llms.txt at celesto.ai, plus Markdown docs in the repository (10). The README's runtime table says when to use each runtime, and the automation section says to prefer exec and keep shell, ssh and desktop for interactive work (14 of 20). Network modes are closed values (open, off, public, restricted) and the SDK takes typed keyword arguments, though internet_settings is a plain dict (11 of 15). Examples directory, a JSON envelope for every command and documented cloud error fields such as required_scope, without a full error catalogue (12 of 15). Dated changelog and tags, pre-1.0 (13 of 15). Total 85.

Deno Sandbox 66

The published OpenAPI document has no sandbox operations, so the typed TypeScript SDK reference on JSR and the typed Python SDK count as 15 of 25 (15). llms.txt and every docs page as Markdown (10). The docs state use cases, when to choose a duration timeout and when to move work to a Deploy app (13). Typed options with stated ranges for memory, capacity and timeout (12). Examples in JavaScript, sync and async Python and the CLI. No error reference was found, and two pages disagree on the default network policy (8). SDKs are versioned at 0.x, and the Deploy changelog's newest entry is 12 March 2026 (8). 15+10+13+12+8+8 = 66.

Agent ergonomics Celesto (formerly SmolVM) +9

Celesto (formerly SmolVM) 69

A CLI and SDK add no tool definitions to an agent's context. Collected command output is capped at 8 MiB with streaming as the alternative (18 of 25). computer list, logs --follow and name lookups, with little filtering (10 of 20). JSON errors carry a recovery command where Celesto has one, and cloud errors carry stable codes, operation and computer context and recovery fields since 0.1.7 (18 of 20). State-changing cloud requests are never replayed automatically and computers are addressed by unique names, but there are no idempotency keys (10 of 20). with Computer() creates and deletes a computer with no parameters, with Python and an alpha TypeScript SDK (13 of 15). Total 69.

Deno Sandbox 60

Sandbox and volume objects are small, and command output streams (15). Lists use cursor pagination with search, label and status filters (15). The Python SDK raises errors with a status, code, message and trace id, and validation errors with a field path, but the codes are not documented (10). No idempotency keys. A duration sandbox can be rejoined by id, and volume slugs are unique per organisation (5). Sandbox.create() needs no parameters, with JavaScript and Python SDKs and a CLI (15). 15+15+10+5+15 = 60.

Security & auth Deno Sandbox +6

Celesto (formerly SmolVM) 52

Framework reading for local software. No credential is needed for local use, and the local API server and dashboard each require a bearer token, and cloud keys carry named permissions (22 of 30). Each computer has its own guest kernel, browser and display access uses capability URLs with a read-only option, and raw VNC is off. Against that, outbound networking is open by default and the restricting modes are opt-in (12 of 20). The security doc warns against giving connection URLs to a model as page content, but there is no guidance on treating command or page output as untrusted (5 of 15). computer logs shows startup output, with no audit log of commands (5 of 15). SECURITY.md with GitHub private vulnerability reporting and a supported-versions table, Security sections in the changelog, no security.txt, bug bounty or certification (8 of 20). Total 52.

Deno Sandbox 58

One organisation token with no scopes or expiry found, rotatable from the dashboard, which also manages the organisation's Deploy apps. All members hold owner permissions (15). An outbound allowlist and read-only volume mounts exist, but outbound access is open unless allowNet is set, per the Security page (13). Secret substitution outside the VM is documented as a defence against prompt injection followed by exfiltration (13). Commands, HTTP requests and SSH sessions are traced in the dashboard with an event log (10). A disclosure policy with safe harbour and a reporting route at security@deno.com, with no acknowledgement time, and a security.txt without an Expires field (7). The SOC2 and ISO27001 claims read on 8 October are no longer on the product or pricing pages, and no bug bounty was found. exposeHttp URLs are public without authentication, which the docs state in capitals. 15+13+13+10+7 = 58.

Score by category

CategoryWeight this runCelesto (formerly SmolVM)Deno SandboxEdge
Reliability16%206643Celesto (formerly SmolVM) +23
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28566Celesto (formerly SmolVM) +19
Agent ergonomics13%16.26960Celesto (formerly SmolVM) +9
Security & auth14%17.55258Deno Sandbox +6
Payments & pricing10%12.56020Celesto (formerly SmolVM) +40
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88145Celesto (formerly SmolVM) +36
Transparency & trust7%8.87067Celesto (formerly SmolVM) +3
Negative events≤150-2
TotalB 68/100D 49.5/100

Facts side by side

FactCelesto (formerly SmolVM)Deno Sandbox
KindSDK + MCPHTTP API
VendorCelesto AI, Inc.Deno Land Inc.
Hosted endpointno (local only)no (local only)
TransportsHTTP
AuthNoneAPI key
PricingFreemiumPaid
x402nono
LicenceApache-2.0Proprietary service under the Deno Deploy terms and conditions. The @deno/sandbox and deno-sandbox SDKs are MIT
Read-only variant documentednoyes
llms.txtyesyes
Last release2026-11-052026-07-22
Terms last updated2026-10-302026-09-30
Privacy policy last updated2026-10-302026-09-30
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessnot found in the textnot found in the text
Terms restrict benchmarkingnot found in the textyes
Terms or service can change without noticenot found in the textyes
Arbitration or class-action waivernot found in the textyes
Popularity1.1k stars, 699 PyPI/wk6 stars, 2k npm/wk

How the scores have moved

Verdicts

Celesto (formerly SmolVM)

Celesto runs each agent task in a local Firecracker or QEMU microVM with its own kernel, driven by a CLI with a stable JSON envelope and a Python SDK, free under Apache-2.0. It is pre-1.0, renamed from SmolVM on 19 September 2026, sends usage telemetry after a first-use notice, and leaves outbound networking open unless a mode is set.

Deno Sandbox

Secrets stay outside the microVM and are substituted only on outbound requests to approved hosts, and an allowlist limits egress. Deno Deploy, which runs it, is due to shut down six months after 9 October 2026, when Deno announced it is joining Cloudflare. The service is still in beta, needs the $20 Pro plan and caps lifetime at 30 minutes.

Before you call either

Celesto (formerly SmolVM)

  1. Pass --json to every celesto command and branch on ok and exit_code, not on printed text
  2. Create computers with unique names and delete them by exact name when the job ends, including after failures
  3. Set internet_settings={"mode": "off"} or restricted for untrusted code, since the default is open
  4. Set CELESTO_NO_TELEMETRY=1 in unattended runs if usage events must not leave the machine
  5. Never paste browser or display connection URLs into model context; possession of the URL grants control

Deno Sandbox

  1. Set DENO_DEPLOY_TOKEN to an organisation token (prefix ddo_) from Settings in console.deno.com. The organisation must be on Pro or above
  2. Pass allowNet on every Sandbox.create(). The Security page says outbound access is unrestricted when it is omitted
  3. Pass credentials through secrets with a hosts list, not env, so code in the VM sees only a placeholder
  4. The default timeout ends the VM when the client disconnects. Pass a duration such as "10m" and reconnect with Sandbox.connect({ id }), up to 30 minutes
  5. Create volumes in ord and start the sandbox in ord. A volume mounts only in its own region
  6. exposeHttp URLs are public with no authentication. Treat the random subdomain as a secret
  7. Plan a move before Deno Deploy closes, six months after 9 October 2026. Deno gives migration support to Cloudflare Workers for paying customers only

Questions

Which is better for AI agents, Celesto (formerly SmolVM) or Deno Sandbox?

Celesto (formerly SmolVM) scores 68 (B) on agent readiness against Deno Sandbox's 49.5 (D), and leads in 6 of 7 scored categories. Deno Sandbox leads on security & auth.

Can an agent call Celesto (formerly SmolVM) and Deno Sandbox without installing anything?

No hosted endpoint is listed for Celesto (formerly SmolVM). No hosted endpoint is listed for Deno Sandbox.

Are Celesto (formerly SmolVM) and Deno Sandbox open source?

Celesto (formerly SmolVM) is open source (Apache-2.0). No open-source release is listed for Deno Sandbox.

Other comparisons with Celesto (formerly SmolVM) or Deno Sandbox

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