Mark Studios Video Toolkit

Convert or retime subtitles (SRT/WebVTT)

convert_subtitles

Read-onlyIdempotent

Converts caption text between SubRip (.srt) and WebVTT (.vtt), optionally shifting every timestamp by a number of milliseconds, and reports format problems (missing numbers, comma/period timestamps, captions run together). Runs entirely on the server with the open-source subtitle code used by the markstudios.com caption tools; nothing is stored.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "captions": "<captions>"
    },
    "name": "convert_subtitles"
  }
}

Input Schema

Name	Required	Description	Default
`to`	No	Output format; 'same' keeps the input format (use with shift_ms or to clean up).	same
`captions`	Yes	The full text of the .srt or .vtt file.
`filename`	No	Original file name, if known; helps tell .srt from .vtt.
`shift_ms`	No	Milliseconds to add to every timestamp (negative moves captions earlier).

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 14, 2026

TDQS

A3.9/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already establish readOnly, idempotent, closed-world and non-destructive. The description goes further by disclosing that processing happens entirely server-side and that nothing is stored, plus that the tool surfaces validation diagnostics (missing numbers, comma vs period timestamps, merged captions) — genuinely useful context beyond the annotation set.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

A single front-loaded sentence with no padding; the core conversion is stated first, then the optional retiming, then the diagnostics and privacy note. It is slightly dense/run-on with the markstudios attribution, but every clause carries information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description carries the return-value burden and does so partially: it says format problems are reported, implying converted text plus a diagnostics list, though the exact shape isn't spelled out. For a stateless four-parameter converter with rich annotations, this is nearly sufficient.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so all four parameters are already documented with defaults, ranges and enum values. The description only echoes the millisecond shift concept and implies that 'same' plus a shift is a valid cleanup mode; it adds little syntax or constraint detail beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

It names a specific verb (converts) and resource (caption text between .srt and .vtt), and adds the two secondary capabilities: timestamp shifting and format-problem reporting. Nothing overlaps with the sibling tools, so an agent can place it immediately.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied: the mention of 'optionally shifting every timestamp' and 'reports format problems' suggests retiming and cleanup scenarios, but the description never states when to pick this over doing nothing or what inputs are unsuitable. No explicit exclusions or preconditions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All Mark Studios Video Toolkit tools Inspect

Try in Browser

One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Glama MCP Gateway

Add one secure layer between your agents and this server.

Resources

Need Help?