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What GitHub changed in September

GitHub's September 9, 2026 announcement introduced central controls that let Copilot Business and Enterprise administrators classify agent operations as blocked, approval-required, or allowed without prompting. The managed rules cover shell commands, file reads and edits, and network domains. A managed restriction cannot be weakened by a user or workspace setting, auto-approval, bypass mode, or a saved approval.

On September 23, GitHub also introduced opt-in local sandboxing in the Copilot app. Per-project settings govern additional read/write, read-only, and denied folders; outbound and local networking; and access to Git and GitHub CLI credentials. The settings apply to new or restarted local sessions, can be narrowed by enterprise policy, and are configured separately from Copilot CLI sandboxing.

Why deterministic validation belongs on the allowlist

An agent can produce syntactically plausible JSON or XML that still violates a schema, uses the wrong type, omits a required property, or breaks a reference-dependent constraint. A deterministic validator gives the workflow a repeatable pass/fail result and focused diagnostics. The agent can correct the specific problem and rerun the same check instead of treating generated text as proof of validity.

This is a good fit for narrow permissions: local validation needs a known executable, a reviewed command shape, and read access to the selected inputs and schema graph. It does not need general shell authority, a writable workspace, or unrestricted internet access.

The valbuddy-cli security model

  • The Agent Plugin contains an MIT-licensed skill and PowerShell wrappers, but no executable, MCP server, hook, background service, downloader, or credential store.
  • The separately installed proprietary valbuddy.exe performs JSON, JSON Schema, and XML validation locally on Windows.
  • Ordinary validation reads selected inputs and schemas and writes no output file.
  • Customer documents are not uploaded to JSONBuddy for ordinary local validation.
  • Wrapper parameter -Offline forwards native valbuddy.exe -offline, which permits local reference graphs but rejects remote $ref, schema, DTD, entity, catalog, import, include, and direct HTTP or HTTPS inputs before connection.
  • Installation and updates use GitHub; downloading the executable and checksum uses www.json-buddy.com. The JSONBuddy Web API is not used for local validation.
  • Core validation is permanently free for commercial and personal use; specifically listed advanced and large-data operations have separate license requirements.

Start with a read-only validation policy

  1. Deploy an reviewed JSONBuddy portable package and record its SHA-256.
  2. Install valbuddy-cli@jsonbuddy from the JSONBuddy-owned marketplace and pin its source to a reviewed full commit SHA when change control requires it.
  3. Allow only the actual PowerShell wrapper with -Offline, or the corresponding valbuddy.exe -offline -v/-wf command prefix observed in your client.
  4. Grant reads only to the project inputs, schemas, and local reference roots required by the workflow.
  5. For ordinary validation, disable outbound and local networking and both credential integrations. Add one write root only for a reviewed generation task.

GitHub documents the policy selectors and precedence, but command strings and paths remain deployment-specific. The canonical deployment guide provides a minimum Copilot app sandbox recipe, a permission matrix, and a placeholder-based managed-settings example without pretending one policy file fits every host.

Install and run an offline validation

copilot plugin marketplace add Clemens-U/jsonbuddy
              copilot plugin marketplace browse jsonbuddy
              copilot plugin install valbuddy-cli@jsonbuddy
              copilot plugin list

Then replace the paths in this prompt: Use valbuddy-cli to validate C:\path\data.json against C:\path\schema.json.

For Visual Studio Code and the GitHub Copilot app, use the JSONBuddy marketplace installation instructions. The plugin is maintained by JSONBuddy; its availability through Copilot does not mean GitHub reviewed, reviewed, certified, or endorsed it.

Put a narrow local check between generation and delivery

Install valbuddy-cli, require native offline mode, approve the exact validation command and project read roots, and keep the host sandbox network-disabled for ordinary local checks.

Install the ValBuddy Agent Plugin