# web_preview_start

Start a web dev server (Next.js, Vite, Flutter Web, Expo Web) for a named workspace app. Returns the iframe URL to embed.

Agent View of the PolicyLayer registry record for `web_preview_start`. HTML page: https://policylayer.com/tools/io-github-kivanccakmak-yaver/web-preview-start

## Facts

- Tool: `web_preview_start`
- Server: Yaver (`yaver-cli`) — https://policylayer.com/tools/io-github-kivanccakmak-yaver.md
- Install: `npx -y yaver-cli`
- Homepage: https://github.com/kivanccakmak/yaver.io
- Risk category: Execute (High risk)
- Registry record: grade F, identity unverified
- Server rate-limited: no
- Parameters: 3
- Recommended policy verdict: Rate-limited

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `app` | string | no | workspace app name |
| `root` | string | no |  |
| `workDir` | string | no | absolute project path (when app is empty) |

Parameters from the server's own tool schema.

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "web_preview_start",
    "arguments": {}
  }
}
```

## Why web_preview_start is rated High

This tool initiates and runs code-execution environments (web dev servers). While not destructive or financial, it executes external processes whose behavior depends on the provided arguments (workspace, app name). An agent could misuse this to start unintended servers, consume resources, or expose ports.

From the tool's own definition: "Tool description states it 'Start[s] a web dev server' which triggers external operations (Next.js, Vite, Flutter Web, Expo Web processes). Starting a development server is code execution with effects dependent on the workspace and app specified as arguments."

## Use case

AI agents invoke web_preview_start to trigger actions in Yaver. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Yaver:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "web_preview_start": {
      "limits": [
        {
          "counter": "web_preview_start_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on Yaver (644)

- `acl_remove_peer` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/acl-remove-peer.md
- `cancel_schedule` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/cancel-schedule.md
- `cloud_destroy` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/cloud-destroy.md
- `companion_down` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/companion-down.md
- `data_delete` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/data-delete.md
- `db_push` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/db-push.md
- `db_reset` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/db-reset.md
- `db_restore` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/db-restore.md
- `dns_flush` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/dns-flush.md
- `dns_remove` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/dns-remove.md
- `docker_prune` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/docker-prune.md
- `docker_rm` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/docker-rm.md
- `docker_rmi` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/docker-rmi.md
- `feedback_delete` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/feedback-delete.md
- `forgot_password` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/forgot-password.md
- `git_member_remove` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/git-member-remove.md
- `git_stash` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/git-stash.md
- `guest_delete` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/guest-delete.md
- `guest_revoke` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/guest-revoke.md
- `jobs_cancel` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/jobs-cancel.md
- `machine_onboarding_remove` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/machine-onboarding-remove.md
- `machine_remove` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/machine-remove.md
- `migrate_rollback` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/migrate-rollback.md
- `models_remove` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/models-remove.md
- `monitor_remove` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/monitor-remove.md
- `phone_project_delete` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/phone-project-delete.md
- `proxy_remove` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/proxy-remove.md
- `relay_clear_password` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/relay-clear-password.md
- `release_rollback` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/release-rollback.md
- `remote_destroy` — Destructive — https://policylayer.com/tools/io-github-kivanccakmak-yaver/remote-destroy.md
- …and 614 more: https://policylayer.com/tools/io-github-kivanccakmak-yaver.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=io-github-kivanccakmak-yaver · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/io-github-kivanccakmak-yaver