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

• 196 MCP tools covering all Rive capabilities, in three tiers — core, standard (the default) and full — chosen with POLYMATION_TOOLS, or switched on per session with enable_tools
• 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

Claude Desktop — one click

• Download rivemcp.mcpb from the latest release.
• Claude Desktop → Settings → Extensions → Install from file… and pick it. No Node.js, no JSON.

Any MCP client (Claude Code, Cursor, Windsurf, VS Code…)

{
  "mcpServers": {
    "polymation": {
      "command": "npx",
      "args": ["-y", "rivemcp"],
      "env": { "POLYMATION_LICENSE_KEY": "your-key" }
    }
  }
}

Installing the package downloads the standalone binary for your platform. The licence key is optional to start: without one, the trial allowance applies. Keys are at polymation.stunning.gg.

Standalone binaries

Windows, macOS (Intel and Apple Silicon) and Linux builds — no Node.js needed — are on the releases page.

Rendering

Previews, GIFs and conversion checks render with Rive's own runtime in a headless Chromium. If a render tool reports that Chromium is missing, run npx playwright install chromium once.

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        the building blocks
  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.

License

Commercial software — see LICENSE. A trial allowance is included; a licence key from polymation.stunning.gg unlocks unlimited use.