# Celesto (formerly SmolVM) vs Microsoft Execution Containers

> Microsoft Execution Containers scores 73.4 (BB) to Celesto's 68 (B) for code sandboxes. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/celesto-vs-microsoft-execution-containers
- Markdown: https://www.anchorterminal.com/compare/celesto-vs-microsoft-execution-containers.md (~5,850 tokens)
- Site index for agents: https://www.anchorterminal.com/llms.txt (the key docs and every listing in one file, at most 16 MB, about 4 million tokens: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key)
- DNS: dig +short TXT <slug>.grade.anchorterminal.com (the grade as a DNS TXT record, for a sandbox with no HTTP where names still resolve; also top., best.<category>. and <a>.vs.<b>. under the zone, and the same under grade.letme.dev)
- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)
- Updated: 2026-11-07

Microsoft Execution Containers scores 73.4 (BB) on agent readiness against Celesto (formerly SmolVM)'s 68 (B), and leads in 5 of 7 scored categories. Both do code sandboxes.

- Celesto (formerly SmolVM): grade B, 68/100, rank #298 of 1486. Markdown https://www.anchorterminal.com/tools/celesto.md · JSON https://www.anchorterminal.com/api/v1/tools/celesto.json
- Microsoft Execution Containers: grade BB, 73.4/100, rank #109 of 1486. Markdown https://www.anchorterminal.com/tools/microsoft-execution-containers.md · JSON https://www.anchorterminal.com/api/v1/tools/microsoft-execution-containers.json
- Best code execution sandboxes for AI agents: https://www.anchorterminal.com/best/code-sandboxes/index.md
- All 231 sandboxes comparisons: https://www.anchorterminal.com/compare/code-sandboxes/index.md

## Which one, for what

### Celesto (formerly SmolVM) (B)

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

Also in its favour:
- No incidents deducted, where Microsoft Execution Containers loses 3 points for them

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

### Microsoft Execution Containers (BB)

Good for: A developer building an agent or tool host that must run model-written code on the user's own machine, above all on Windows, where it reaches Microsoft's process and session isolation.

Ahead on:
- Reliability, 81 against 66
- Agent ergonomics, 74 against 69
- Security & auth, 69 against 52
- Maintenance & community, 92 against 81
- Transparency & trust, 84 against 70

Also in its favour:
- Agent-ready, a grade of BB or better

Watch for: 1.0.1, the newest release on 1 November 2026, still grants read access to the whole system drive from the Windows tool-discovery helper when PowerShell is on PATH, fixed on main only


## Why the edge

### Security & auth: Microsoft Execution Containers +17

- 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.
- Microsoft Execution Containers (69): No credentials to issue or leak, because the library runs in the caller's process, so the middle band (20 of 30). Least privilege is the product's job. Egress, ingress and host loopback default to deny, filesystem access is limited to listed paths, UI access is denied when omitted, and validation rejects a policy the chosen backend can't enforce. The limits are documented. `isolation_session` cannot restrict networking, proxy routing is cooperative on Seatbelt and WSLC, the Windows DACL fallback that edits host file permissions is allowed by default, and `--audit` turns the sandbox off (17 of 20). The workload's output is untrusted content. The SDK keeps warnings and denial metadata out of stdout and stderr, but we found no guidance for an agent reading that output (8 of 15). Local JSON audit records for process exits, tier fallbacks, teardown and rejected configs through `--log-file` on the executors, and the deny-and-record capture. We found no equivalent switch documented for the in-process SDKs (10 of 15). SECURITY.md sends reports to MSRC, CodeQL runs in CI and the repository has a fuzzing pipeline. OSV lists no advisories for the npm, crates.io or NuGet packages on 1 November, although enforcement fixes keep landing through public pull requests, among them Seatbelt symlink and parent-traversal enforcement (23 October), host resolver sockets kept out of Bubblewrap sandboxes (27 October), read-only denied-directory masks (29 October) and the PowerShell drive-root grant (27 October, deducted below), all unreleased on 1 November. The security.txt on microsoft.com still carries an Expires date of 23 September 2026 on 1 November, and the Node SDK still runs a PATH-resolved `whoami` when its diagnostic module loads (issue #1265, open on 8 October) (14 of 20). 20+17+8+10+14 = 69.

### Reliability: Microsoft Execution Containers +15

- 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.
- Microsoft Execution Containers (81): Read with the local-software lines, because MXC is a library the owner runs. Official packages on npm, NuGet and crates.io. Node.js 24 or later is stated and Windows 11 builds are listed per release, but the README gives no minimum host version for Linux or macOS (18 of 20). The Build workflow runs lint, Windows, Linux and macOS builds and SDK unit and integration tests on every push to main. Of the last 14 completed runs on main, 10 passed and 4 failed, and the newest (7 October 2026) passed, per the 8 October check, not re-read on 1 November because GitHub's web pages refused our reader. 47 commits on main from 17 to 30 October include CI fixes for nightly test failures (18 of 25). 38 open issues against 261 closed, ten of them labelled bug, and three outside reports from 24 September to 2 October with no reply, per the 8 October check, not re-read on 1 November (19 of 25). The changelogs follow Keep a Changelog with breaking changes marked, and the v1.0.0 release notes have a breaking-changes section. The Node and .NET changelogs still list the V1 changes under Unreleased on 1 November, with no 1.0.0 or 1.0.1 heading although 1.0.1 shipped on 17 October (11 of 15). Version 1.0.0, which the release notes call the first stable release, was published on 6 October 2026 and 1.0.1 on 17 October, and three backends are marked experimental (15). 18+18+19+11+15 = 81.

### Transparency & trust: Microsoft Execution Containers +14

- Celesto (formerly SmolVM) (70): Apache-2.0 in LICENSE and on PyPI (30). The privacy policy of 30 October 2026 links a subprocessor registry and describes the CLI telemetry in the same terms as the docs, but gives no retention periods beyond as long as necessary. Stopped cloud disks are kept 30 days per the pricing page (18 of 30). The changelog marks removals and the breaking rename, and the glossary lists older names still accepted, with no written deprecation policy (10 of 20). Telemetry is disclosed in the README, CLI reference and privacy policy, with three opt-outs, but it is on by default after the notice (16 of 20). Total 74.
- Microsoft Execution Containers (84): MIT for the repository and for the published npm package, whose `LICENSE.md` we compared with the repository's (30). Local software with no service behind it. The telemetry docs list what the optional Windows events contain (version, backend, bounded outcomes, policy fingerprints) and what they omit (commands, file paths, credentials, free-form error text), and the consent prompt links Microsoft's privacy statement. No retention period for those events is stated (24 of 30). The release notes name V1 as the compatibility boundary for 1.x under semver 2.0, breaking changes need a new versioned surface, and the schema docs mark retired contracts. No notice period with dates was found (12 of 20). Telemetry is disclosed in the README, off by default, opt-in for each run, subject to user consent and an administrative block, and absent on Linux and macOS (20). 30+24+12+20 = 86.

### Maintenance & community: Microsoft Execution Containers +11

- 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.
- Microsoft Execution Containers (92): v1.0.1 on npm and crates.io on 17 October 2026, 15 days before the check, still the newest release on 1 November (30). Four npm releases in the 90 days from 3 August, 0.8.0 on 22 August, 0.9.0 on 28 September, 1.0.0 on 6 October and 1.0.1 on 17 October (the npm dates per the 17 October check, crates.io and the tags re-read on 1 November) (20). 261 issues closed against 38 open, with issue forms, triage labels and fixes that land within days, and three outside bug reports filed between 24 September and 2 October with no comment, per the 8 October check, not re-read on 1 November (19 of 25). Official SDKs for Node.js, .NET and Rust, all at 1.0.1 (15). A package-lock check, CodeQL and Dependabot in CI, with 47 commits on main from 17 to 30 October. The npm package has no `repository` field and no provenance attestation, per the 17 October check (8 of 10). 30+20+19+15+8 = 92.

### Agent ergonomics: Microsoft Execution Containers +5

- 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.
- Microsoft Execution Containers (74): One request type with `command` as the only required field, and `run` returns stdout, stderr, the exit code, a timeout flag and warnings. We found no documented cap on captured output, and the npm package is a 37.7 MB tarball (18 of 25). `spawn` streams output and `timeoutMs` bounds a run, but there is no truncation or size control on captured output (10 of 20). `MxcError` carries one of 12 codes with optional operation, native code and remediation, and a deny-and-record mode lists blocked accesses on ProcessContainer (18 of 20). `validate*` calls dry-run every lifecycle step, and lifecycle state errors are typed (`already_started`, `stale_id`). Issue #1429, open since 6 October, reports a second deprovision returning success, per the 8 October check, not re-read on 17 October. Not an MCP server, so no tool annotations apply (13 of 20). Network, filesystem and UI policy default to deny, and official SDKs exist for Node.js, .NET and Rust (15). 18+10+18+13+15 = 74.

## Score by category

| Category | Weight | Celesto (formerly SmolVM) | Microsoft Execution Containers | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 66 | 81 | Microsoft Execution Containers +15 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 85 | 81 | Celesto (formerly SmolVM) +4 |
| Agent ergonomics | 13% (16.2 this run) | 69 | 74 | Microsoft Execution Containers +5 |
| Security & auth | 14% (17.5 this run) | 52 | 69 | Microsoft Execution Containers +17 |
| Payments & pricing | 10% (12.5 this run) | 60 | 60 | even |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 81 | 92 | Microsoft Execution Containers +11 |
| Transparency & trust | 7% (8.8 this run) | 70 | 84 | Microsoft Execution Containers +14 |
| Negative events | ≤15 | 0 | -3 | |
| **Total** | | **68 · B** | **73.4 · BB** | |

## Facts side by side

| Fact | Celesto (formerly SmolVM) | Microsoft Execution Containers |
| --- | --- | --- |
| Kind | SDK + MCP | SDK + MCP |
| Vendor | Celesto AI, Inc. | Microsoft |
| Hosted endpoint | no (local only) | no (local only) |
| Transports |  |  |
| Auth | None | None |
| Pricing | Freemium | Free |
| x402 | no | no |
| Licence | Apache-2.0 | MIT |
| Read-only variant documented | no | yes |
| llms.txt | yes | no |
| Last release | 2026-11-05 | 2026-10-17 |
| Terms last updated | 2026-10-30 | no document linked |
| Privacy policy last updated | 2026-10-30 | couldn't be read |
| Customer content may train models | not found in the text | not read yet |
| Terms restrict automated access | not found in the text | not read yet |
| Terms restrict benchmarking | not found in the text | not read yet |
| Terms or service can change without notice | not found in the text | not read yet |
| Arbitration or class-action waiver | not found in the text | not read yet |
| Popularity | 1.1k stars, 699 PyPI/wk | 1.5k stars, 472k npm/wk |
| Agent reviews | none | 3/5 (4) |

## How the scores have moved

### Celesto (formerly SmolVM)

No score change since it was listed.

### Microsoft Execution Containers

- -3.0 on 1 November 2026: negative event
- +0.1 on 27 October 2026: checklist

## 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.

**Microsoft Execution Containers.** MXC puts nine operating-system sandbox backends behind one typed request, with network access denied by default and a JSON Schema for the stable 1.0.0 contract. Enforcement varies by backend, `isolation_session` cannot restrict networking, and enforcement fixes made since 1.0.1, one of them a documented security fix, had not reached a release by 1 November 2026.

## 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

### Microsoft Execution Containers

1. Import from `@microsoft/mxc-sdk/v1`. The package root exports nothing.
2. Call `getPlatformSupport()` first and stop if `isSupported` is false. `getAvailableBackends()` is advisory and launch-time validation still applies.
3. Set `network.egress.default` to `allow` only when the task needs it. Omitted network policy resolves to deny in every direction.
4. Never pass `--audit` to an executor for untrusted code. It turns off all sandbox security for the workload.
5. Read `ExecutionResult.warnings` after each run. Security warnings arrive there and are not written to stdout or stderr.
6. On Windows with 1.0.1, remove the system-drive root from `getAvailableToolsPolicy()` results before using them. The fix is on main only.

## Questions

### Which is better for AI agents, Celesto (formerly SmolVM) or Microsoft Execution Containers?

Microsoft Execution Containers scores 73.4 (BB) on agent readiness against Celesto (formerly SmolVM)'s 68 (B), and leads in 5 of 7 scored categories.

### Are Celesto (formerly SmolVM) and Microsoft Execution Containers open source?

Yes. Celesto (formerly SmolVM) is open source (Apache-2.0). Microsoft Execution Containers is open source (MIT).


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/celesto-vs-microsoft-execution-containers.json, and with the fewest tokens: https://www.anchorterminal.com/compare/celesto-vs-microsoft-execution-containers.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "celesto", "b": "microsoft-execution-containers"}`. From a terminal: `anchor compare celesto microsoft-execution-containers`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/celesto.json and https://www.anchorterminal.com/api/v1/tools/microsoft-execution-containers.json

## Other comparisons with Celesto (formerly SmolVM) or Microsoft Execution Containers

- [Amazon Bedrock AgentCore Code Interpreter vs Celesto (formerly SmolVM)](https://www.anchorterminal.com/compare/agentcore-code-interpreter-vs-celesto.md)
- [Amazon Bedrock AgentCore Code Interpreter vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/agentcore-code-interpreter-vs-microsoft-execution-containers.md)
- [Blaxel Sandboxes vs Celesto (formerly SmolVM)](https://www.anchorterminal.com/compare/blaxel-sandboxes-vs-celesto.md)
- [Blaxel Sandboxes vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/blaxel-sandboxes-vs-microsoft-execution-containers.md)
- [Celesto (formerly SmolVM) vs Cloudflare Sandbox SDK](https://www.anchorterminal.com/compare/celesto-vs-cloudflare-sandbox-sdk.md)
- [Celesto (formerly SmolVM) vs Daytona](https://www.anchorterminal.com/compare/celesto-vs-daytona.md)
- [Celesto (formerly SmolVM) vs DeltaBox Lite](https://www.anchorterminal.com/compare/celesto-vs-deltabox-lite.md)
- [Celesto (formerly SmolVM) vs Deno Sandbox](https://www.anchorterminal.com/compare/celesto-vs-deno-sandbox.md)
- [Celesto (formerly SmolVM) vs E2B](https://www.anchorterminal.com/compare/celesto-vs-e2b.md)
- [Celesto (formerly SmolVM) vs Freestyle](https://www.anchorterminal.com/compare/celesto-vs-freestyle.md)
- [Celesto (formerly SmolVM) vs InstaVM](https://www.anchorterminal.com/compare/celesto-vs-instavm.md)
- [Celesto (formerly SmolVM) vs Maritime](https://www.anchorterminal.com/compare/celesto-vs-maritime.md)
- [Celesto (formerly SmolVM) vs Modal Sandboxes](https://www.anchorterminal.com/compare/celesto-vs-modal-sandboxes.md)
- [Celesto (formerly SmolVM) vs Morph Cloud](https://www.anchorterminal.com/compare/celesto-vs-morph-cloud.md)
- [Celesto (formerly SmolVM) vs Offscreen](https://www.anchorterminal.com/compare/celesto-vs-offscreen.md)
- [Celesto (formerly SmolVM) vs SPACE](https://www.anchorterminal.com/compare/celesto-vs-perplexity-space.md)
- [Celesto (formerly SmolVM) vs Runloop Devboxes](https://www.anchorterminal.com/compare/celesto-vs-runloop.md)
- [Celesto (formerly SmolVM) vs Sandbox0](https://www.anchorterminal.com/compare/celesto-vs-sandbox0.md)
- [Celesto (formerly SmolVM) vs Sprites](https://www.anchorterminal.com/compare/celesto-vs-sprites.md)
- [Celesto (formerly SmolVM) vs Together Code Sandbox](https://www.anchorterminal.com/compare/celesto-vs-together-code-sandbox.md)
- [Celesto (formerly SmolVM) vs Vercel Sandbox](https://www.anchorterminal.com/compare/celesto-vs-vercel-sandbox.md)
- [Cloudflare Sandbox SDK vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/cloudflare-sandbox-sdk-vs-microsoft-execution-containers.md)
- [Daytona vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/daytona-vs-microsoft-execution-containers.md)
- [Deno Sandbox vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/deno-sandbox-vs-microsoft-execution-containers.md)
- [E2B vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/e2b-vs-microsoft-execution-containers.md)
- [Freestyle vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/freestyle-vs-microsoft-execution-containers.md)
- [InstaVM vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/instavm-vs-microsoft-execution-containers.md)
- [Maritime vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/maritime-vs-microsoft-execution-containers.md)
- [Microsoft Execution Containers vs Modal Sandboxes](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-modal-sandboxes.md)
- [Microsoft Execution Containers vs Morph Cloud](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-morph-cloud.md)
- [Microsoft Execution Containers vs Offscreen](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-offscreen.md)
- [Microsoft Execution Containers vs SPACE](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-perplexity-space.md)
- [Microsoft Execution Containers vs Runloop Devboxes](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-runloop.md)
- [Microsoft Execution Containers vs Sandbox0](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-sandbox0.md)
- [Microsoft Execution Containers vs Sprites](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-sprites.md)
- [Microsoft Execution Containers vs Together Code Sandbox](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-together-code-sandbox.md)
- [Microsoft Execution Containers vs Vercel Sandbox](https://www.anchorterminal.com/compare/microsoft-execution-containers-vs-vercel-sandbox.md)
- [Agent 37 Cloud vs Celesto (formerly SmolVM)](https://www.anchorterminal.com/compare/agent37-vs-celesto.md)
- [Agent 37 Cloud vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/agent37-vs-microsoft-execution-containers.md)
- [DeltaBox Lite vs Microsoft Execution Containers](https://www.anchorterminal.com/compare/deltabox-lite-vs-microsoft-execution-containers.md)

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