crv-guide

get_frames

Retrieves additional keyframes from an already analyzed video to inspect specific moments by start index and frame count.

Instructions

Fetch more keyframes from a video already analysed with watch_video.

Args: source: The same URL or path given to watch_video. start_index: 1-based index of the first frame to return. count: How many frames to return (1-24).

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": {
      "source": "<source>"
    },
    "name": "get_frames"
  }
}

Input Schema

Name	Required	Description	Default
`count`	No
`source`	Yes
`start_index`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 23, 2026

TDQS

A3.7/5.0

Behavior3/5

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

No annotations exist, so the description carries the full burden. It usefully discloses that source must match the value passed to watch_video, that indexing is 1-based, and that count is capped at 24, but it says nothing about what happens if the video was never analysed or about the shape of the returned frames.

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?

The leading sentence front-loads the core purpose, and the Args block is compact. The raw docstring formatting ('Args:' with indentation) leaks through and is slightly less scannable than prose, but no sentence is wasted.

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

Completeness3/5

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

For a three-parameter read tool with no annotations and no output schema, the description should establish what comes back (image data, URLs, thumbnails) and what happens at the end of a video's frame list. The pagination parameters are covered, but the return shape is entirely undocumented anywhere.

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

Parameters4/5

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

Schema coverage is 0%, yet the description documents all three parameters with meaning the schema does not carry: the source must be the identical URL/path from watch_video, start_index is 1-based, and count has a 1-24 range. It loses a point only for not restating the default of 12 or the frame-count limits of the underlying video.

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

Purpose4/5

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

States a specific verb and resource ('Fetch more keyframes from a video') and anchors it to a prerequisite operation (watch_video), which cleanly separates it from the sibling that does the initial analysis. It stops short of the 5 because it never says what a returned frame actually is.

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

Usage Guidelines4/5

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

The phrase 'from a video already analysed with watch_video' gives an explicit precondition and points to the sibling that must run first. There is no statement of when not to use it or of get_transcript as an alternative for non-visual needs.

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

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