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), authors Spline 3D scenes (.splinecode / .spline), and converts between Rive, Spline, Lottie, Figma and After Effects — with an honest per-decision loss report and real-runtime validation before you ship. Exposed as MCP tools for LLM-driven animation authoring.

Format support

Format	Author	Convert	Status
Rive — .riv / .rev	✅	↔ Spline, ↔ Lottie, → Figma	Live
Spline — .splinecode / .spline	✅	↔ Rive, ↔ Lottie, → Figma	Live
Lottie — .lottie / .json	—	↔ Rive, ↔ Spline, → Figma	Live
Figma	—	→ Rive / Spline / Lottie	Live
After Effects — .aep	edit only	→ Rive / Lottie / Spline / Figma	Live

Every conversion crosses a model boundary, so every one is lossy — the report says what came across clean, what was reconstructed, what was dropped and what needs your call. After Effects is read natively (no After Effects install, no plugin) and can be edited and saved back; writing a .aep from scratch is not offered, because without After Effects there is no way to check such a file would open.

Features

• 193 MCP tools covering all Rive capabilities (55 in the core tier, 116 in standard; set POLYMATION_TOOLS=core|standard|full)
• 290 Rive runtime types — full coverage of the Rive binary format
• Spline 3D authoring — generate .splinecode (runtime) and .spline (editor) scenes from scratch
• Cross-format conversion — Rive ↔ Spline ↔ Lottie, plus Figma and After Effects in, each with a per-decision loss report (clean / reconstructed / dropped / needs-your-call) and runtime validation
• After Effects projects read natively — .aep compositions, layer timing and parenting, keyframes with AE's own ease curves, shapes, paths, masks, gradients, text and effects; edit_aep writes changes back
• 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.