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by CarlxsMG
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add_widget_animation_keyframe

Add a keyframe to an existing widget animation property track at a specified time, choosing linear, cubic, or constant interpolation.

Instructions

Add a keyframe to an existing widget-animation property track's section (call add_widget_animation_track first). Converts time_seconds to an FFrameNumber via the MovieScene's tick resolution, extends the section's range to cover the key if needed, then adds the key on the matching channel(s) via the requested interpolation (AddLinearKey | AddCubicKey | AddConstantKey for float/color's FMovieSceneFloatChannel(s); bool channels have no interpolation concept and always use UpdateOrAddKey).

Returns: { widget_bp_path: string, animation_name: string, widget_name: string, property_path: string, track_type: string, time_seconds: float, key_frame: int, keys_added: int, interpolation: string, saved: bool, save_error: string }

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
forceNoOptional. This command is REFUSED while a Play-in-Editor session is running: it either compiles a Blueprint (the reinstancer can retain a world, and CheckForWorldGCLeaks is Fatal -- it KILLS the editor) or writes to disk (Editor.AllowSavingAssetsDuringPIE=0 makes the engine refuse the write, so it would report success without writing a byte). Stop PIE and retry instead; force=true runs it anyway, at your own risk.
valueNokey value: a number for float, a bool for bool, or a [R,G,B,A] (A optional, defaults 1.0) array for color
widget_nameYesname of the animated widget
time_secondsYestime (seconds, >= 0) at which to place the key
interpolationNoOptional "linear" (default) | "cubic" | "constant" (float/color only; ignored for bool)
property_pathYesthe SAME property_path used in add_widget_animation_track
animation_nameYesobject name OR display label of the target animation
blueprint_nameNoAlias of `widget_bp_path` (same value, same meaning). Accepted because sibling tools spell this parameter differently; prefer `widget_bp_path`.
widget_bp_pathNo/Game path of the Widget Blueprint asset

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.1.0

TDQS

A4.3/5.0
Behavior4/5

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

Annotations only declare generic flags (readOnly=false, idempotent=false, destructive=false), so the description carries real weight: it discloses the internal conversion of time_seconds to an FFrameNumber, the side effect of extending the section's range to cover the key, and how channel type drives interpolation (bool channels always use UpdateOrAddKey, which also explains the non-idempotent hint). It omits the on-disk save behavior, though the returns block implies it.

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 purpose and prerequisite are front-loaded, and the dense technical clause about conversion, range extension, and channel dispatch is informative rather than padded. It is a single long sentence plus a returns block, which is slightly heavy but every clause carries signal.

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?

For a 9-parameter mutation tool with no output schema, the description covers the prerequisite, the side effects, the channel-type semantics, and even enumerates the return fields, so the agent has most of what it needs. Missing is explicit mention of the PIE-refusal constraint (delegated to the schema's force parameter) and the disk-save implication.

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 100%, so the baseline is 3. The description goes beyond the schema by explaining that time_seconds is converted via the MovieScene's tick resolution and by mapping the interpolation values to concrete channel calls (AddLinearKey/AddCubicKey/AddConstantKey, with bool channels having no interpolation), which adds genuine semantic meaning for two parameters.

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?

The description names a specific verb+resource ('Add a keyframe to ... a widget-animation property track's section') and clearly distinguishes itself from the sibling add_widget_animation_track by stating it requires that tool to have run first. An agent can tell it apart from generic keyframe siblings like add_keyframe_to_property_track because it is scoped specifically to widget-animation tracks.

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?

It states the ordering prerequisite explicitly ('call add_widget_animation_track first'), which tells the agent when this tool is applicable. It does not, however, contrast itself against the analogous sequence keyframe tools or state exclusions (e.g., bool-channel interpolation being ignored), leaving some routing to inference.

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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