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Preflight

by allthepossibles.com · remote · no sign-in to list tools · v1.0.0 · published by com.allthepossibles

Scans an MCP server for security gaps before your agent connects. Free tier, no signup.

Changes · 4
CompareRegistry entry

4 tools: 4 change things.

Scanned Oct 21, 2026

2 checks matched something in the tool definitions. No finding is not a safety guarantee. How the checks work.

claude mcp add --transport http preflight https://preflight.allthepossibles.com/mcp

Findings

Matches of fixed checks, with the text they matched.

2 info

Tools

Open a tool for its reasons and full description. Descriptions are the publisher's own words, shown as they are.

4 tools

Changes things 4Claude Code: ask
  • check_outputCheck a structured output you're about to return or act on for degenerate-answer patterns a schema check can't see: invalid JSON, a placeholder value ('TBD', 'N/A', 'unknown') wher…No findings

    Why it is in this group

    • Nothing in its name or description says what it does, so it is counted as a write.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
    Description, as the server wrote it
    Check a structured output you're about to return or act on for degenerate-answer patterns a schema check can't see: invalid JSON, a placeholder value ('TBD', 'N/A', 'unknown') where a real answer should be, an array of byte-identical items (a common symptom of a loop that never advanced), or an expected field that's missing or empty. Schema validity and answer quality are different guarantees, call this before trusting your own output, not just after validating it parses.

    Annotations the server declares

    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: false
  • scan_contentCheck a document or web page for hidden instructions before an agent reads, summarizes, or acts on it: invisible Unicode, obfuscated payloads, and (on Pro) a semantic pass for prom…No findings

    Why it is in this group

    • Nothing in its name or description says what it does, so it is counted as a write.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
    Description, as the server wrote it
    Check a document or web page for hidden instructions before an agent reads, summarizes, or acts on it: invisible Unicode, obfuscated payloads, and (on Pro) a semantic pass for prompt-injection phrasing aimed at the model instead of the human reader. Pass either a URL to fetch, or raw text you already have.

    Annotations the server declares

    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: true
  • scan_extensionCheck a VS Code extension or a Claude Skill before installing or trusting it.1 finding

    Why it is in this group

    • Nothing in its name or description says what it does, so it is counted as a write.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.

    Findings

    • Info

      The description mentions "credential".

      Matched text

      description: "...engine scan_content uses), unscoped or credential-referencing tool grants in its allowed-..."

      What this check looks for
    Description, as the server wrote it
    Check a VS Code extension or a Claude Skill before installing or trusting it. For a VS Code extension (which runs with full Node.js access and no permission model to scope): publisher domain-verification status weighed against install count, and known-bad-signature checks on its description. For a Claude Skill: hidden-instruction and obfuscated-payload detection on the SKILL.md body (the same engine scan_content uses), unscoped or credential-referencing tool grants in its allowed-tools/disallowed-tools frontmatter, inline shell execution baked into the file itself, and pattern matching on any bundled script files for credential-exfiltration signatures. Semantic prompt-injection detection on a skill's body runs too on Pro.

    Annotations the server declares

    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: true
  • scan_mcp_serverCheck an MCP server for real risk signals before trusting it: unauthenticated transport, capability overreach (filesystem/shell/credential access with no scoping), and known-bad si…1 finding

    Why it is in this group

    • Nothing in its name or description says what it does, so it is counted as a write.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.

    Findings

    • Info

      The description mentions "credential".

      Matched text

      description: "...capability overreach (filesystem/shell/credential access with no scoping), and known-bad..."

      What this check looks for
    Description, as the server wrote it
    Check an MCP server for real risk signals before trusting it: unauthenticated transport, capability overreach (filesystem/shell/credential access with no scoping), and known-bad signatures. Pass a live server URL, or a manifest of tool definitions if the server isn't reachable over HTTP. Semantic prompt-injection detection runs too if a Pro API key is sent as an Authorization: Bearer header, see /docs.

    Annotations the server declares

    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: true

This is not a safety rating, and no finding is not a safety guarantee. The groups and findings come from fixed checks of the tool definitions the server returned on the date shown, not from its code or what it does when called. How the checks work.

Install

Pinned to version 1.0.0. Values in angle brackets are yours to fill in.

claude mcp add --transport http preflight https://preflight.allthepossibles.com/mcp

Run in a terminal.

Claude Code permissions

Allow the reads, ask before a change, deny the deletes. Paste into .claude/settings.json.

.claude/settings.json
{
  "permissions": {
    "allow": [],
    "ask": [
      "mcp__preflight__scan_mcp_server",
      "mcp__preflight__scan_content",
      "mcp__preflight__scan_extension",
      "mcp__preflight__check_output"
    ],
    "deny": []
  }
}

Tools that only read are allowed, tools that change things ask first, tools that delete or cancel are denied. It assumes the server is installed as preflight. Review it before you use it.