Render preview
render_previewShow what a Blender scene looks like: a fast, low-cost preview render on a cloud GPU, back as an image in seconds. Typical requests: 'render this .blend', 'show me the scene', 'preview the turntable', 'I have no GPU', 'Blender is too slow on my laptop', 'Blenderでレンダリングして', 'GPUがない', 'ターンテーブル', '商品の360度動画'. Also use it after writing a bpy script, to see what it builds. Each preview returns a critic verdict (ok / check / fix) with fix code: apply the fixes and preview again before any final render. It also returns final_estimate (the same scene as a 1080p final) and quota_left_today; tell the user both before asking to go on. Prices come before rendering: final_offers give each next render's time and price, and a paid one needs the user's approval. A script that raises comes back as a failure with the line (nothing is rendered). When not to use: editing a scene open in the user's Blender belongs to a local Blender MCP, and a single still on a machine with its own NVIDIA GPU usually renders faster locally. This service is for CPU-only machines, animations, and scripts with no Blender installed. Limits: up to 1280x720; 1-4 frames tiled in one labeled image for the GPU time of one 720p frame. preset='product' | 'turntable' | 'animation' sets camera, light, backdrop and frames for that purpose. Other options are explained on each parameter: environment presets and 'compare', orbit (turntable), cameras (several named cameras), engine, transparent, asset_urls with 'polyhaven:' CC0 assets. Give the scene as scene_script (bpy code as text), scene_url (an https link to a .blend, .py or 3D file) or scene_id; reuse the returned scene_id in render_final. variations=[{label, environment, environment_strength, camera, colors}, ...] (2-8): the same frame once per variant, rendered in parallel and tiled in one sheet labelled A, B, ...; anything a variant leaves out uses this call's settings. colors maps an object name to '#rrggbb' (or [r, g, b, a], 0-1) for its material's Principled Base Color. GPU time is the sum of the variants. Show the sheet, ask the user to pick one, then call render_final with that variant's render_final args. Not with cameras, orbit or environment='compare'.
Tool call template
This tool declares no required parameters. Add optional parameters from the input schema as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {},
"name": "render_preview"
}
}Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| orbit | No | True: turntable; an orbit camera circles the scene once (the scene's own camera is not used). Flat floors and walls are ignored when framing. A preview without frames shows 0/90/180/270 degrees; a final without frame_end renders the whole turn as an MP4. Best for imported models and product videos. | |
| width | No | Output width in pixels (previews are capped at 1280x720 keeping the aspect ratio; a final frame can have at most 1920x1080 pixels on free time, 3840x2160 on prepaid credit). | |
| camera | No | Name of the camera object to render from (default: the scene's active camera, or an automatic camera if there is none). Ignored with orbit=True; not combinable with cameras. | |
| engine | No | '' or 'cycles' (path tracing, default) | 'eevee' (real-time rasterizer: about two-thirds of the Cycles per-frame cost on longer animations; every GPU chunk pays about 7-9 s of loading and shader compilation, so below about 100 frames Cycles is usually as cheap or cheaper, and previews stay on Cycles). | |
| frames | No | Preview frames: '' = frame 1; '12' = one frame; '1,8,16,24' or '1-24' = up to 4 frames tiled in one labeled image (to judge camera motion and animation; same GPU time as one 720p frame). | |
| height | No | Output height in pixels (previews are capped at 1280x720 keeping the aspect ratio; a final frame can have at most 1920x1080 pixels on free time, 3840x2160 on prepaid credit). | |
| preset | No | Purpose preset: 'product' (4 studio shots at 0/90/180/270 deg on a plain backdrop; the final gives 4 PNGs at 1440x1440), 'turntable' (one full turn as an MP4, studio light, plain backdrop), 'animation' (the scene's own camera, lights and frame range; the scene is read first when the range is unknown), or '' (none). It fills what you do not pass; environment, orbit_frames, width/height and the frames still win when given. | |
| blender | No | Blender version: '' (default: a .blend opens with the version it was saved in, other scenes with 5.0) or '5.0' / '5.2' / '5.3' (also '4.5', '4.2', '3.6'; a script that stops on Blender 5 because of an older API is rendered again on those automatically) to choose. | |
| cameras | No | Several camera object names (up to 8) rendered from the same frame in one job: the preview tiles them in one labeled sheet, the final returns one PNG/EXR per camera (camera_files maps names to files). For product shots from fixed angles. Not combinable with orbit, environment='compare' or camera. | |
| samples | No | Cycles samples per pixel (preview: up to 32, default 16; final: default 128). | |
| scene_id | No | scene_id returned by an earlier call (reuses the uploaded scene without sending it again). | |
| full_turn | No | True with orbit=True (or preset='turntable'): preview the whole turn as up to 24 small frames in one sheet (labelled in degrees) instead of 4 angles; leave frames out. Preview only. | |
| scene_url | No | https link to a .blend, a .py script or a 3D file (.glb/.gltf/.fbx/.usd/.obj/.stl/.ply/.abc; a Gaussian splat .spz or 3DGS .ply opens with Blender 5.3); the service fetches it (e.g. the sample https://render.janction.jp/samples/cube_scene.py, or a 12-hour /upload link). A .gltf or .obj also brings its .bin / .mtl / textures from the same folder. | |
| asset_urls | No | Extra files sent with the scene: https links (textures, glTF .bin) or 'polyhaven:<id>' CC0 assets from asset_search ('polyhaven:<id>@2k' for 2k textures). A .blend finds them through relative paths (same folder); a script through os.environ['JR_ASSETS_DIR'] or the jr_assets helpers. | |
| variations | No | 2-8 variants of the same frame, each {label, environment, environment_strength, camera, colors}; rendered in parallel and tiled in one sheet labelled A, B, ... Leave empty for a normal preview. | |
| draft_video | No | True for an animation: preview the whole frame range as a small, quick draft: up to 24 frames spread over the range, tiled in sheet.png and played over the real length in draft.mp4 (the reply's draft section). Leave frames out. The reply's final_estimate is the time and price of every frame at full quality. | |
| environment | No | Lighting preset: '' (the scene's own world), 'studio', 'sunset', 'overcast' or 'night' (bundled HDRIs; a good first render for scenes without lighting work), or 'compare' (preview only: all four in one labeled 2x2 image, to pick one). | |
| transparent | No | True renders on a transparent background (alpha) for product shots and overlays; png / exr / webm / gif / webp keep it, mp4 and prores cannot. The preview sheet shows it over dark grey. | |
| orbit_frames | No | Number of frames for one full turn (default 24). | |
| orbit_target | No | Object name or 'x,y,z' to centre the orbit on (default: the scene's main objects). | |
| scene_script | No | The scene as bpy Python code (text). No file and no local Blender needed; the service runs it in Blender 5.0 (5.2 or 5.3 with blender='5.2' / '5.3'). Blender 5.0 API notes: materials are node-based, so set a colour on the Principled BSDF (mat.node_tree.nodes['Principled BSDF'].inputs['Base Color'].default_value = (r, g, b, 1)); mat.diffuse_color only affects the viewport; do not set Material.use_nodes. Animate with obj.keyframe_insert() (action.fcurves no longer exists; set bpy.context.preferences.edit.keyframe_new_interpolation_type = 'LINEAR' first for constant speed). Build the scene, camera and frame range only; leave resolution, samples and denoising to the service. Helpers: `import jr_assets`, then jr_assets.frame_camera(margin=1.1) points the camera at every object and fits them in the frame; jr_assets.import_model('<id>'), jr_assets.material('<id>') and jr_assets.world_hdri('<id>') use Poly Haven assets passed in asset_urls. | |
| orbit_distance | No | Multiplier for the orbit camera distance (default 1.0). | |
| orbit_elevation | No | Orbit camera elevation in degrees (default 18). | |
| environment_visible | No | False hides the HDRI from the camera (flat grey backdrop, HDRI lighting only). | |
| environment_strength | No | Multiplier for the HDRI preset's brightness (default 1.0). |