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ass_load_keyframes

Loads video keyframes into workspace.keyframes in milliseconds from a media file, frame numbers, or explicit times, enabling timing work in Aegisub subtitle documents.

Instructions

Load video keyframes into workspace.keyframes (milliseconds).

Args: path: media file. When omitted the workspace video is probed with render.keyframes. doc_id: document id; only used as an fps source when frames is given. frames: explicit frame numbers to convert (needs an fps). times_ms: explicit keyframe times in milliseconds — used verbatim.

Returns: {"source", "path", "count", "keyframes_ms", "first_ms", "last_ms"}

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
pathNo
doc_idNo
framesNo
times_msNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A3.6/5.0
Behavior3/5

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

With no annotations, the description carries the full burden. It discloses the state mutation (writing into workspace.keyframes) and the probing side effect when path is omitted, plus the response keys. It does not say whether existing keyframes are overwritten or what permissions/setup are needed, so behavioral coverage is partial.

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?

Front-loaded purpose sentence followed by clearly labeled Args and Returns blocks; every line is short and functional. The Returns block is partially redundant given an output schema exists, but it does not bloat the definition.

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?

An output schema exists so return values need not be spelled out, and all four optional parameters are documented despite 0% schema coverage. No annotations exist to cover behavior, and the description leaves overwrite semantics unstated, which is the only notable gap for a 4-parameter workspace-mutating tool.

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 description coverage is 0%, so the description must compensate, and it does: all four parameters are explained with meaning and interdependencies (doc_id acts only as an fps source when frames is given; frames needs an fps; times_ms is used verbatim). Only the 'source' concept and accepted value formats (e.g., frame types) are left implicit.

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: 'Load video keyframes into workspace.keyframes (milliseconds)', including the destination and unit. It clearly reads keyframes from a video, distinguishing it from sibling utilities like ass_snap_to_keyframes (which presumably consumes them), though it does not name that sibling explicitly.

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?

The Args section implicitly guides calling modes (omit path to probe the workspace video; frames requires an fps; times_ms is verbatim), which is prerequisite-style guidance. However, it never states when to use this tool versus alternatives such as ass_snap_to_keyframes or ass_read_timecodes, so routing remains inferred.

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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