rivemcp

Polymation

The multi-format AI animation MCP — one MCP for every animation format. Polymation is the most complete Rive MCP (it generates binary .riv runtime and .rev editor files from scratch via a high-level builder API), and it authors Spline 3D scenes (.splinecode / .spline) and converts Rive↔Spline both ways — with an honest per-decision loss report and real-runtime validation before you ship. On the roadmap: Lottie (.lottie/bodymovin → editable Rive), Figma, and After Effects (.aep). Exposed as MCP tools for LLM-driven animation authoring.

Format support

Format	Author	Convert	Status
Rive — .riv / .rev	✅	✅ ↔ Spline	Live
Spline — .splinecode / .spline	✅	✅ ↔ Rive	Live
Lottie — .lottie / .json	—	→ editable Rive	Roadmap
Figma	—	→ Rive / Spline	Roadmap
After Effects — .aep	—	→ runtime formats	Roadmap

Features

• 168 MCP tools covering all Rive capabilities
• 290 Rive runtime types — full coverage of the Rive binary format
• Spline 3D authoring — generate .splinecode (runtime) and .spline (editor) scenes from scratch
• Rive ↔ Spline conversion — bidirectional, with a per-decision loss report (clean / reconstructed / dropped / needs-your-call) and runtime validation
• Import + roundtrip — load existing .riv files, modify, re-export
• Edit tools — query, update, and delete objects after creation
• 14 easing presets — ease, spring, bounce, material design, and more
• Physics engine — compile-time gravity, bounce, wind, and spring forces
• Prefab library — rocks, dust, sparks, rain, snow, leaves, backgrounds
• Scene composer — describe a full animated scene in JSON, get a .riv in one call

Quick Start

One-click install for Claude Desktop (recommended)

• Download rivemcp-<version>.mcpb from the Releases page.
• Open Claude Desktop → Settings → Extensions → Install from file...
• Select the .mcpb file. Done — no Node.js, no JSON editing, no path setup.

Manual install (other MCP clients)

npm install
npm run build

Add to your MCP client configuration:

{
  "mcpServers": {
    "rivemcp": {
      "command": "node",
      "args": ["dist/mcp/server.js"]
    }
  }
}

Or run in development mode:

npm run dev

Building the .mcpb bundle yourself

npm run build:mcpb

Produces rivemcp-<version>.mcpb in the repo root (~7 MB). Distribute that single file for one-click install.

Tool Categories

Category	Tools	Description
Artboard	3	Create projects, artboards, list objects
Shapes	9	Rectangles, ellipses, triangles, paths, groups
Style	7	Fills, strokes, gradients, trim paths, dash paths, feather
Edit	6	Query, update, and delete shapes/groups/text
Animation	3	Keyframe animation with 14 easing presets
State Machine	12	Layers, states, transitions, conditions, listeners
Events	3	Custom events, open-URL events, custom properties
Text	3	Text objects with styled runs
Images	2	Embedded image assets
Nested	4	Nested artboards for component reuse
Bones	6	Bones, IK constraints, skinning
Mesh	1	Mesh deformation
Constraints	1	Transform constraints
Scroll	2	Scroll and scroll-bar constraints
ViewModel	12	Data enums, view models, instances, data binding
Advanced	44	Layout, assets, scripting, organization, draw order
HLAPI	8	Physics baking, prefabs, particles, scene composition
Import/Export	2	Load existing .riv, export with validation

Easing Presets

The add_keyframe tool accepts an easing parameter for named presets:

Preset	Curve	Use Case
linear	Constant speed	Rotation, continuous motion
ease	Gentle S-curve	General purpose
ease-in	Slow start	Elements leaving view
ease-out	Slow end	Elements entering view
ease-in-out	Slow both ends	Symmetric transitions
material-standard	Material Design	Navigation transitions
material-decelerate	Material decel	Incoming elements
material-accelerate	Material accel	Outgoing elements
spring	Overshoot	Playful interactions
bounce-out	Settle bounce	Landing, drop effects
snap	Fast then hold	Toggle, switch states
anticipate	Pull-back start	Button press, launch
smooth	Smooth S-curve	UI transitions
smooth-out	Smooth decel	Fade-in
smooth-in	Smooth accel	Fade-out

High-Level Animation API (HLAPI)

Three abstraction layers for complex animations:

Layer 3: Scene Composer    compose_scene
  "Rockslide with mountains, 20 falling rocks, dust"

Layer 2: Prefabs           spawn_prefab, emit_particles
  "Spawn 20 rocks with random size/position"

Layer 1: Physics Bakers    bake_motion, bake_shake
  "Apply gravity, bounce at ground, wind gusts"

Layer 0: Core Tools        132 MCP tools
  Shapes, fills, keyframes, state machines...

Physics Forces

• Gravity — constant downward acceleration
• Ground bounce — collision with restitution and squash/stretch
• Wind — horizontal force with sinusoidal gusting
• Spring — Hooke's law oscillation toward an anchor point

Physics runs at compile time. Dense per-frame snapshots are compressed to sparse keyframes via Douglas-Peucker simplification (180 frames typically compress to 5-10 keyframes).

Prefab Library

Shapes: rock, dust_cloud, debris, spark, raindrop, snowflake, leaf, bubble Backgrounds: sky_gradient (day/dusk/night/storm), mountain_range, ground_plane, starfield

Edit Tools

Six tools for iterative design after initial creation:

Tool	Description
get_object_info	Query any object's transform, geometry, fills, strokes
update_object	Modify position, size, rotation, scale, opacity
update_fill	Change fill color by index
update_stroke	Change stroke color, thickness by index
remove_object	Delete a shape, group, or text
update_text	Update text content on a run

Import / Roundtrip

load_riv → modify with tools → export_riv

The load_riv tool imports existing .riv files into the builder scene graph. Unmodified artboards are preserved byte-for-byte on re-export.

Demo Files

File	Description
sample.riv	Basic shapes + keyframe animation
expand-rect.riv	State machine click interaction
ui-buttons.riv	Full UI dashboard: gradients, elastic easing, blend states, feather, trim paths
flag-wave.riv	Mesh deformation + embedded image
confetti-twist.riv	Mesh corner spiral animation
rockslide-hlapi.riv	HLAPI physics, prefabs, and scene composition
character-demo.riv	Bones, IK constraints, skinning
data-bind-demo.riv	Toggle switch with cross-object color theme change

Generate demos with:

npx tsx scripts/generate-sample.ts
npx tsx scripts/generate-ui-buttons.ts
npx tsx scripts/generate-data-bind-demo.ts

Viewer

Open viewer.html in a browser (via HTTP server) to preview .riv files. Supports drag-and-drop upload and a batch test grid for all demo files.

npx serve .
# Open http://localhost:3000/viewer.html

Development

npm test              # Run all tests
npm run build         # TypeScript compile
npm run dev           # Run MCP server with tsx
npm run extract-defs  # Regenerate rive-defs.json from rive-cpp

Architecture

src/
  core/           Binary .riv reader/writer, LEB128 encoding
  defs/           Rive type registry (from rive-cpp source)
  builder/        High-level scene graph API
  hlapi/          Physics engine, prefab library, scene composer
  mcp/            MCP server + 132 tools

License

All rights reserved. Commercial license required for use.