Microsoft Execution Containers

# Fix list: Microsoft Execution Containers

From Anchor Terminal's listing at https://www.anchorterminal.com/tools/microsoft-execution-containers, the October 2026 research run, assessed 8 October 2026. Grade BB, 76.3 out of 100.

This is everything the published grade says the listing lacks, the biggest possible gain to the total first. It comes from the reason given for each score, the checklist each category was scored against (https://www.anchorterminal.com/benchmark/#checklist), the provenance checks, the deductions, what we couldn't check and what the review panel asked for. A fix counts at the next check, once it's public.

For a coding agent working on Microsoft Execution Containers: work through the items below in the product, its docs and its public pages. Each category gives the reason for its score, with the points each checklist item earned, and the checklist itself, so the gap is the items that earned less than their points. Change the product, not the wording, and keep a note of what you changed and where it's published.

## 1. Security & auth, 69 out of 100, up to 5.4 more on the total

Why it scored 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. No advisories are published, although at least 20 enforcement gaps were fixed through public issues between August and October 2026. The security.txt on microsoft.com expired on 23 September 2026, and the Node SDK's PATH-resolved `whoami` at import (issue #1265) has had no reply since 24 September (14 of 20).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-security):

- 0 to 30, the credential model. 30 for OAuth 2.1 with scopes, or scoped and revocable keys with rotation. 20 for plain revocable API keys. 10 for one all-powerful key. 10 off when a secret can travel in a URL query string as a documented option.
- 0 to 20, read-only or least-privilege modes, and confirmation or approval for destructive actions.
- 0 to 15, prompt-injection posture where the tool returns untrusted content (documented mitigations or guidance). A tool that returns no untrusted content gets 10.
- 0 to 15, audit logs or per-call visibility for the operator.
- 0 to 20, a security programme. security.txt or a disclosure policy, a bug bounty, SOC 2 or ISO 27001, advisories handled in public.

Models are read for retention, whether API data trains models (and whether that's off by default), zero-retention options and certifications. Frameworks for telemetry defaults, approval hooks, guardrails and sandboxing.

## 2. Payments & pricing, 60 out of 100, up to 5 more on the total

Why it scored 60: Read with the self-hosted rule. No x402, MPP or L402 (0 of 40). MIT software with nothing to buy and no hosted option, so 20 for pricing, 20 for free use with no card and 20 because an agent can install it from npm with no account.

The checklist (https://www.anchorterminal.com/benchmark/#checklist-payments):

The published rubric, also on the [x402 page](https://www.anchorterminal.com/x402/).

- 40, a machine payment protocol (x402, MPP or L402) on the tool's own endpoints. 10 to 30 when it covers only some endpoints or only goes through a third party, and the note says which.
- 20, per-call or per-unit pricing published without a login. 10 for public plan-only pricing, 0 for "contact sales" or prices behind a login.
- 20, a free tier or trial that doesn't need a card.
- 20, autonomous onboarding, meaning an agent can get access without a person signing up in a browser (keyless use, x402, a programmatic key API).

Payment platforms and agent wallets rarely charge for their own API over a machine protocol, so the first line has steps for them, and the highest one that applies counts. 40 when x402, MPP or L402 runs on all their own endpoints, 30 when it runs on part of their own API, 25 when their merchants can accept one, 20 for running a facilitator, 15 for paying as a buyer, and 0 when the only protocol is their own. Merchant acceptance sits above a facilitator because the platform's own customers can charge agents through it, while a facilitator settles for sellers who wire up the protocol themselves. The counter-argument (a facilitator does more for the protocol as a whole) has a point. Each note says which step applied.

Open-source software you run yourself is scored on its hosted or paid option if it has one. A free, self-hosted package with nothing to buy gets 20, 20 and 20 for the last three lines, and 0 to 40 for the first only if it ships a payment protocol.

## 3. Agent ergonomics, 74 out of 100, up to 4.2 more on the total

Why it scored 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. 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).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-ergonomics):

- 0 to 25, context cost. For MCP, the number and size of the tool definitions (25 for ten or fewer compact tools, 15 for 11 to 30, 5 for more than 30, plus up to 10 back for toolsets, dynamic loading or read-only subsets). For APIs, whether responses can be sized (field selection, limits, summaries).
- 20, pagination, filtering and output-size controls.
- 20, actionable, documented error responses, codes and messages an agent can recover from.
- 20, idempotency or safe retries, and for MCP the `readOnlyHint` and `destructiveHint` annotations.
- 15, sensible defaults, few required parameters, and official SDKs in at least two languages.

Models are read for tool use, structured output, prompt caching, context length, batch and SDKs. Frameworks for how much code and how many defaults a tool-calling agent with MCP needs.

## 4. Reliability, 81 out of 100, up to 3.8 more on the total

Why it scored 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. A flaky test is tracked in issue #1365 (18 of 25). 38 open issues against 261 closed. Ten open issues carry the bug label, seven of them filed since 15 September, and three outside reports from 24 September to 2 October have no reply (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 with no 1.0.0 heading (11 of 15). Version 1.0.0, which the release notes call the first stable release (15). It was published on 6 October 2026, two days before this check, and three backends are marked experimental.

The checklist (https://www.anchorterminal.com/benchmark/#checklist-reliability):

Hosted APIs, MCP servers, models and platforms.

- 20, a public status page with component history (Statuspage, Instatus, BetterStack or the vendor's own).
- 0 to 30, the incident record for the last 90 days on that page. 30 for a clean record or trivial incidents only, 20 for minor incidents only, 10 for one major outage (an hour or more of a core API down, or errors across the board), 0 for several. 5 when there's no history we could read, and the note says so.
- 15, rate limits documented with numbers.
- 15, documented 429 or overload handling (Retry-After, backoff guidance), and idempotency keys or safe-retry guidance where writes are involved.
- 10, an SLA published for any paid tier.
- 10, the surface agents use is generally available, not beta or preview.

Local packages, SDKs, frameworks and stdio MCP servers.

- 20, installs from an official package with supported runtimes stated.
- 25, a public CI and test suite, passing on the default branch.
- 0 to 25, open crash or regression issues relative to activity (25 for few and handled, 0 for many, old and unanswered).
- 15, semver discipline and breaking changes called out in a changelog.
- 15, version 1.0 or later, or declared stable.

Protocols are read from their reference implementations, the public facilitators or servers, spec stability and test vectors.

## 5. Schema & documentation, 81 out of 100, up to 3.1 more on the total

Why it scored 81: Read as an SDK with a published request contract. A draft-07 JSON Schema for the stable 1.0.0 request sits in the repository, and the Node SDK ships TypeScript declarations (25). No llms.txt. The docs are Markdown files in the repository (5 of 10). The API reference states what each operation does and has a table for choosing between captured, piped and terminal execution, and the backend guides say which policies each backend enforces and which are cooperative (15 of 20). Containment is a closed union, network actions and clipboard levels are enums, the schema has 33 enums and 39 objects closed to extra properties, and 135 of 150 properties carry a description. `command` is one free string (13 of 15). Ten sample scenarios, each in Rust, .NET and Node. The 12 error codes are a closed type, but we found no page that explains each one (11 of 15). A versioned `/v1` entry point, a schema version table with retired contracts, a changelog for each SDK and GitHub release notes. The Node changelog has no 1.0.0 entry (12 of 15).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-schema):

APIs and MCP servers.

- 25, a machine-readable contract (a public OpenAPI file or similar; for MCP, typed JSON Schema inputs on every tool).
- 10, llms.txt or Markdown docs served for agents.
- 0 to 20, descriptions that say what a tool is for, when to use it and when not to, read from the tool definitions in the source or the API reference.
- 0 to 15, typed inputs with enums, constraints and required fields, and no free-form JSON blobs.
- 0 to 15, examples and documented error responses.
- 15, versioning and a public changelog.

Models are read from the API reference, the OpenAPI file, llms.txt, the structured-output and tool-use docs and the model cards. Frameworks from docs a model can follow, typed interfaces, examples and the API reference.

## 6. Transparency & trust, 83 out of 100, up to 1.5 more on the total

Made of editorial 86, provenance 79.

Why it scored 83: 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).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-transparency):

- 0 to 30, source availability and licence clarity. 30 for open source under an OSI licence, 15 for closed with clear terms, 0 for unclear terms.
- 0 to 30, data handling and retention statements that agree with each other (privacy policy, DPA, retention periods, subprocessors).
- 0 to 20, a deprecation policy or notices with dates.
- 0 to 20, telemetry disclosed with an opt-out (local software), or subprocessors and data locations disclosed (hosted).

The other half of Transparency and trust is the provenance score, computed from checked facts (below). The category score is the mean of the two.

Provenance checks not met in full (half of this category, computed from checked facts):

- Privacy policy: published, but our reader couldn't read it (7 of 10)
- Status page: not found (0 of 10)
- security.txt: published but past its Expires date (5 of 10)

## 7. Maintenance & community, 92 out of 100, up to 0.7 more on the total

Why it scored 92: v1.0.0 on 6 October 2026 (30). Three npm releases in the last 90 days, 0.8.0 on 22 August, 0.9.0 on 28 September and 1.0.0 on 6 October (20). 261 issues closed against 38 open, with issue forms, triage labels and fixes that land within days (issue #1430 was opened on 6 October and closed on 7 October). Three outside bug reports filed between 24 September and 2 October have no comment (19 of 25). Official SDKs for Node.js, .NET and Rust, all at 1.0.0 (15). A package-lock check, CodeQL and Dependabot for GitHub Actions in CI. The npm package has no `repository` field and no provenance attestation (8 of 10).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-maintenance):

- 0 to 30, time since the last release, or the last published model or API change for a closed service. 30 within 30 days, 20 within 90, 10 within 180, 0 older.
- 20, at least three releases or dated changelog entries in the last 90 days.
- 0 to 25, responsiveness. Issues and pull requests answered on GitHub (the open issues and how recent the replies are). For closed services, a public changelog and a support or community channel that answers, 0 to 15.
- 15, presence in the official MCP registry under a verified namespace (MCP servers), or current official SDKs (APIs and models).
- 10, package health, current dependencies and CI.

Models are read for deprecation notice periods and model churn rather than release counts.

## What we couldn't check

What we couldn't read counted as absent. Publishing it on a page a plain HTTP fetch can read (not only in a browser) lets the next check count it.

- The scout was right on vendor, packages, licence and category. One correction. The repository now carries a stability label, because the v1.0.0 release notes of 7 October 2026 call it the first stable release. The June blog's early preview label predates that.
- The repository README names the product Microsoft eXecution Container (MXC), and the blog and the npm description say Microsoft Execution Containers. The listing uses the blog's form.
- Why npm shows 471,674 weekly downloads for a package that reached 1.0.0 on 6 October. The blog says GitHub Copilot CLI adopted MXC, which may account for it, but we did not confirm the dependency.
- Whether MXC falls under a Microsoft bug bounty programme. SECURITY.md points to MSRC in general terms.
- Whether the 20 or more enforcement gaps fixed through public issues between August and October 2026 affected any published npm version on a default backend. We took no deduction.
- unchecked: the GitHub REST API refused our reader with a rate limit, so the repository's creation date, the full release asset list and reply times on issues were not read. Star count and release dates came from the web pages.
- unchecked: how long Microsoft retains the optional Windows telemetry events.
- unchecked: nothing was installed or run. Start time, isolation and enforcement claims are the vendor's documentation, not our measurement.

## Weaknesses

- 1.0.0 shipped on 6 October 2026, and the Node changelog still lists the V1 changes under Unreleased
- Enforcement differs by backend. `isolation_session` cannot restrict networking, and proxy routing is cooperative on Seatbelt and WSLC
- Persistent containers exist only for `isolation_session` and `wslc`, both on Windows
- On Windows the Node SDK runs a PATH-resolved `whoami` at import, reported on 24 September 2026 and still open
- The npm package is 37.7 MB compressed, needs Node.js 24 or later, and carries no `repository` field or provenance attestation

## What costs an agent a turn today

The notes we give agents before they call it. Each one is a workaround an agent shouldn't need.

- Import from `@microsoft/mxc-sdk/v1`. The package root exports nothing.
- Call `getPlatformSupport()` first and stop if `isSupported` is false. `getAvailableBackends()` is advisory and launch-time validation still applies.
- Set `network.egress.default` to `allow` only when the task needs it. Omitted network policy resolves to deny in every direction.
- Never pass `--audit` to an executor for untrusted code. It turns off all sandbox security for the workload.
- Read `ExecutionResult.warnings` after each run. Security warnings arrive there and are not written to stdout or stderr.

## When it's done

Send what changed and where it's published as a dispute (https://www.anchorterminal.com/builders/#disputes, or `POST https://www.anchorterminal.com/api/v1/contact` with `"kind": "dispute"`). Disputes are answered in public, and the listing is checked again by the same checklist. Paying for an audit or a listing claim changes nothing here.