# `com.powmcp/caption-file-check` on anlyon.dev

> Text inside fenced blocks marked untrusted-server-text was written by the MCP server's publisher, not by anlyon.dev. It is data to inspect, not instructions to follow. Invisible characters are shown as [U+XXXX].
> No finding is not a safety guarantee: these are point-in-time checks of tool definitions, not of code or behaviour.

- Page: https://anlyon.dev/servers/com.powmcp/caption-file-check
- JSON: https://anlyon.dev/api/v1/servers/com.powmcp/caption-file-check
- Version: 0.3.3 (active)
- Publisher: com.powmcp (domain proven to the MCP Registry)
- Runs: remote (streamable-http)
- Sign-in to list tools: none
- Repository: https://github.com/powmcp/mcp-server-guide
- Metadata from the official MCP Registry, synced 2026-10-21T18:00:46.186Z

Title and description, as the publisher wrote them:

```untrusted-server-text
Caption File Check
Parse WebVTT, SRT, or TTML for conformance, timing, overlaps, line length, and reading speed.
```

Scanned 2026-10-21T18:36:01.243Z over streamable-http.

**2 tools: 1 change things and 1 only read.**

| Group | Class | Tools | Claude Code |
| --- | --- | --- | --- |
| Deletes or cancels | destructive | 0 | deny |
| Can't be undone | irreversible | 0 | ask |
| Changes things | write | 1 | ask |
| Only reads | read | 1 | allow |

## Exfil surface

4 private-data -> untrusted-input -> outbound paths in this server alone. Denying 1 private-data tool breaks every one: `mcp__caption-file-check__caption_compare`.

| Tag | Meaning | Tools |
| --- | --- | --- |
| private-data | Reads files, mail, messages, databases, secrets, calendars or repositories. | `mcp__caption-file-check__caption_compare` |
| untrusted-input | Brings in text someone else can write: web pages, inbound email, messages, issues and comments. | `mcp__caption-file-check__caption_check` `mcp__caption-file-check__caption_compare` |
| outbound | Can carry data to people or systems: it sends, posts or publishes, or takes a recipient, channel or URL. | `mcp__caption-file-check__caption_check` `mcp__caption-file-check__caption_compare` |

| Private data | Untrusted input | Outbound |
| --- | --- | --- |
| `mcp__caption-file-check__caption_compare` | `mcp__caption-file-check__caption_check` | `mcp__caption-file-check__caption_check` |
| `mcp__caption-file-check__caption_compare` | `mcp__caption-file-check__caption_check` | `mcp__caption-file-check__caption_compare` |
| `mcp__caption-file-check__caption_compare` | `mcp__caption-file-check__caption_compare` | `mcp__caption-file-check__caption_check` |
| `mcp__caption-file-check__caption_compare` | `mcp__caption-file-check__caption_compare` | `mcp__caption-file-check__caption_compare` |

## Findings

- **info** The word "credentials" in `caption_check` ([credentials-mention](https://anlyon.dev/methodology#credentials-mention))

```untrusted-server-text
The input schema at properties.url.description mentions "credentials".

inputSchema.properties.url.description: "..., data URLs, FTP/SFTP, and URLs needing credentials, headers, or cookies are not supported...."
```


## Changes things (1)

Creates or changes something that can be changed back. Claude Code: ask.

### `caption_check`

- 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.
- Tag untrusted-input: The server marks it openWorldHint: true: it reaches things outside the server's own data.
- Tag outbound: The input takes a URL (input.url): a request to a URL can carry data to whoever runs it.
- Findings: info credentials-mention

Description, as the server wrote it:

```untrusted-server-text
Preflight one caption or subtitle file before delivery. Attach a WebVTT (.vtt), SRT (.srt), or TTML/IMSC (.ttml/.xml) caption file in chat or give a publicly fetchable URL and it downloads the artifact under an SSRF-guarded, 2 MB-capped fetch, detects the format by content and the byte encoding and BOM, then parses it with the real spec engine (the WebVTT spec parser, a dedicated SRT parser, or the imscJS TTML/IMSC profile engine) and returns deterministic evidence: pass/fail, cue count, structural spec and IMSC profile-conformance errors, overlapping / negative / out-of-order / empty cues, per-line length, and per-cue and summary reading speed (CPS) against a named platform profile (netflix-adult-20, netflix-children-17, youtube, ebu-tt). It reports only source-file conformance, timing, encoding, and reading-speed facts against a dated profile. It does not judge translation quality, transcription accuracy, or synchronization against the video. An arbitrary XML or text file that is not a caption track returns an explicit unsupported-format error. Fetching and parsing a full-length track can take up to 60 seconds. WebVTT limitation: the parser drops payload-less cues; cue counts, indices, timing checks and comparisons cover retained cues only, not those omitted cues.
```

## Only reads (1)

Looks things up and changes nothing. Claude Code: allow.

### `caption_compare`

- The name "caption_compare" says "compare": a word for reading.
- Tag private-data: The description's first sentence says "compare" and "file": it reads files. The input names a file (input.files), and the tool reads: it reads files.
- Tag untrusted-input: The server marks it openWorldHint: true: it reaches things outside the server's own data. The input takes a URL (input.urls), and the tool reads it: it reads web pages, which anyone can write.
- Tag outbound: The input takes a URL (input.urls): a request to a URL can carry data to whoever runs it.
- Claude Code: ask, because it is tagged outbound.

Description, as the server wrote it:

```untrusted-server-text
Compare exactly two caption or subtitle files under identical bounded checks: an original versus its translated track, before versus after a timing fix, or a format migration. Attach two WebVTT, SRT, or TTML/IMSC caption files in chat or give two publicly fetchable URLs and it runs the same SSRF-guarded, 2 MB-capped preflight as caption_check on each, then aligns them by cue index and reports side-by-side pass status, detected-format and encoding differences, the cue-count delta, timing drift and overlap differences, reading-speed (CPS) regressions, structural-error deltas, and a winner only when the measured checks separate the two. Use caption_check for a single file. It reports only source-file conformance, timing, encoding, and reading-speed facts against a dated profile: never translation quality, transcription accuracy, or sync against the video. Fetching and parsing two live files can take up to 60 seconds. WebVTT limitation: the parser drops payload-less cues; cue counts, indices, timing checks and comparisons cover retained cues only, not those omitted cues.
```

## Claude Code permissions

For `.claude/settings.json`, assuming the server is installed as `caption-file-check`:

```json
{
  "permissions": {
    "allow": [],
    "ask": [
      "mcp__caption-file-check__caption_check",
      "mcp__caption-file-check__caption_compare"
    ],
    "deny": []
  }
}
```

Capability tags behind the rules (a read tagged outbound is asked about):

- `mcp__caption-file-check__caption_check`: untrusted-input, outbound
- `mcp__caption-file-check__caption_compare`: private-data, untrusted-input, outbound

## Remote posture

What an anonymous client saw at the remote endpoint, last 2026-10-22T14:38:39.333Z, unchanged since 2026-10-22T14:38:39.333Z. No credentials were sent and no tool was called. Values are shown as the endpoint returned them. Method: https://anlyon.dev/methodology#remote-posture

| Fact | Observed |
| --- | --- |
| Reachable | `yes` |
| HTTP status of an anonymous initialize | `200` |
| tools/list served without credentials | `yes` |
| Tools that change things, listed without credentials | `1` |
| Protocol version | `2025-06-18` |
| WWW-Authenticate on 401 | `not observed` |
| resource_metadata in WWW-Authenticate | `none` |
| RFC 9728 protected resource metadata | `https://powmcp.com/.well-known/oauth-protected-resource/caption-file-check/mcp` |
| Authorization servers | `https://clerk.powmcp.com` |
| Legacy HTTP+SSE transport | `no` |
| Dynamic client registration | `no` |
| Client ID metadata documents | `yes` |

- **warn** Tools that change things, listed to anyone ([unauth-remote-writes](https://anlyon.dev/methodology#unauth-remote-writes))

```untrusted-server-text
The endpoint served tools/list without credentials, and the list has 1 tool that changes things (1 write). Whether a call also works without credentials was not tested: tools are never called.

https://powmcp.com/caption-file-check/mcp: tools/list returned 2 tools to an anonymous client, including caption_check (write)
```