Render Preview
render_previewUse this when you need to LOOK at a kernelCAD model — render its script to deterministic PNG views for visual self-check (the visual half of the evaluate → render → inspect → fix loop), with NO studio or dev server required. Pass { code } (inline source) or { file } (a .kcad.ts path), exactly one. Renders the canonical engineering views (front, right, top, iso — pass { views } for a subset, e.g. ["iso"] for fastest iteration) plus an optional { pose: "," } arbitrary camera angle (degrees; az=0,el=0 is front, +az rotates CCW around +Z, +el lifts the camera). NO STUDIO / DEV-SERVER REQUIRED: a prebuilt static player (dist/headless-player) is served from an ephemeral local port automatically; a running studio dev server is used as fallback, and { base_url } forces one. The only environment dependency is playwright chromium (npx playwright install chromium). Pass { focus } or { hide } (arrays of feature ids or assembly part names, mutually exclusive) to isolate parts — same semantics as kernelcad render --focus/--hide. Pass { section: { axis, position, flip? } } to cut a cross-section and inspect INTERIOR geometry (wall thickness, internal pockets, whether a bore runs through) rather than only the outer shell. Pass { explode: { factor, mode? } } to pull a multi-part assembly apart (mode: "mate-axis" default, or "radial") using the same mesher as kernelcad render --explode — requires assembly.model()/solvedModel(). PNGs are written to { out_dir } (default: a fresh temp session directory) and returned as absolute paths with per-view camera descriptions (kernelCAD is Z-up). Mechanism truth runs first, same protocol as kernelcad render: a broken mechanism still renders but every tile is watermarked MECHANISM BROKEN (KERNELCAD_RENDER_STRICT=1 refuses instead); read { mechanism, mechanism_failure_codes }. The probe runs full BREP interference sweeps and can dominate latency on large assemblies — pass { no_mechanism_check: true } for fast iteration (the preview then reports mechanism: "unverified"; ignored under strict mode). Pass { overlay: 'zebra' | 'curvature' | 'continuity' } for a surface-quality visualisation (zebra stripes from vertex normals, curvature as vertex colours, continuity edges coloured by G0/G1/G2/broken) — numbers come from inspect({ of: 'continuity' | 'curvature' }); the overlay is the picture. PUBLISH PRESET: pass { preset: 'publish' } for a share-ready studio product shot (gallery tile, social post, README image, product page): key/fill/rim lights + room reflections, soft contact shadow, clean backdrop ({ background: 'white' (default) | 'light' | 'dark' | 'black' | '#rrggbb' | 'transparent' } — transparent gives a PNG with alpha), { shadow: false } to drop the shadow, 2× supersampled anti-aliasing, 30° lens, the model silhouette centred and auto-framed with ~11% air (a script's setCameraTarget is ignored), per-part colours/materials as authored, no watermark. With no views/pose it renders ONE image named 'hero' (3/4 front-right, az=30°, el=22°) at 1600×1200; width/height go up to 2048; views/pose still work under the preset. Output is deterministic for the same input. For a 360° loop use capture_animation({ turntable: true }). INSPECTION SHEET: { sheet: true } renders all seven views (iso, front, back, left, right, top, bottom) and adds one labelled image named 'sheet' tiling them — do not call a model done because it compiled; call it done when every tile of the sheet matches the request. Returns { ok, images: [{ name, path, description }], out_dir, bounds, mechanism, render_source, render_ms, diagnostics }. PATHS ARE LOCAL to the machine running the MCP server — local stdio clients read them directly; hosted/remote clients should use open_in_studio instead.
Hosted server: the PNGs come back IN the result as image content (up to ~1.5 MB total; larger sets are link-only) and each images[i].url is an HTTPS link that expires after 24 h. images[].path is a server-side path you cannot open. Works without saving a project (autosave:false is fine). Hosted: lib.fromSTEP / fromSTL / meshFromSTL / fromDXF / fromSVG and referenceImage take a direct string literal or a const bound to one (computed expressions are unsupported). They accept "asset:" (from request_upload), an https:// URL or a data: URI as the path.
Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| code | No | Inline kernelCAD script source. Mutually exclusive with file. Relative imports resolve against a temp dir — use file for scripts with relative lib.fromSTEP(...) imports. | |
| file | No | Path to a .kcad.ts script on disk. Mutually exclusive with code. Hosted server: cannot read files from your machine — pass `code`, or `project:<slug>` for a saved project. | |
| hide | No | Hide matching feature ids / assembly part names. Mutually exclusive with focus. | |
| pose | No | Extra arbitrary camera pose '<az>,<el>' in degrees, e.g. '30,20'. | |
| focus | No | Show only matching feature ids / assembly part names. Mutually exclusive with hide. | |
| sheet | No | Also write one labelled image 'sheet' tiling every rendered view. With no views it renders all seven (adds back, left, bottom) — use it before calling a model done, so a missing cutout on the back or underside is not missed. | |
| views | No | Canonical views to render as an array, e.g. ["iso"] or ["front","top"] (default: all four). Fewer views = faster. | |
| width | No | Per-view tile width in px (default 768; 1600 under preset: 'publish'). | |
| height | No | Per-view tile height in px (default 768; 1200 under preset: 'publish'). | |
| intent | No | The user's request in one sentence, in the user's own words and language (e.g. 'M4 bracket for a 25 mm tube, print on Bambu A1'). Helps kernelCAD improve; leave out personal data. | |
| preset | No | Render look: 'default' (engineering review) or 'publish' (studio product shot for sharing; one 'hero' image unless views/pose are given). | |
| shadow | No | preset 'publish' only: soft contact shadow under the model (default true). | |
| explode | No | Pull a multi-part assembly apart for the preview. factor ≥ 0 scales spacing by part size; mode is 'mate-axis' (default, along parent mate/joint axes) or 'radial' (away from the assembly centroid). Requires the script to return assembly.model() / solvedModel(). | |
| out_dir | No | Directory for the PNGs (created if missing). Default: a fresh temp session dir. | |
| overlay | No | Surface-quality overlay: 'zebra' (reflection stripes), 'curvature' (Gaussian vertex colours), 'continuity' (edges coloured G2 green / G1 yellow / G0 orange / broken red). Built as coloured STL bands through this same pipeline. | |
| section | No | Cut the model with one axis-aligned section plane to inspect INTERIOR structure (wall thickness, internal pockets, whether a bore runs through) instead of only the outer shell. position is in mm along the axis (kernelCAD Z-up frame); flip keeps the +axis side (default keeps the -axis side). | |
| shading | No | Mesh shading: 'smooth' uses the kernel's vertex normals (default); 'flat' uses face normals to expose tessellation / surface wobble. | |
| base_url | No | Advanced: force a specific render server (e.g. a running studio dev server) instead of the bundled static player. | |
| background | No | preset 'publish' only: 'white' (default), 'light', 'dark', 'black', 'transparent' (PNG alpha), or '#rrggbb'. | |
| environment | No | HDRI environment override: preset ('studio', 'softbox', 'neutral', 'outdoor', 'warehouse'), a URL, or 'none' for the default three-light rig. | |
| no_watermark | No | Suppress the kernelCAD version watermark. | |
| no_mechanism_check | No | Skip the mechanism-truth probe for fast iteration on large assemblies; the preview reports mechanism: 'unverified'. Ignored under KERNELCAD_RENDER_STRICT=1. | |
| screenshot_timeout_ms | No | Playwright screenshot deadline in milliseconds. Default leaves Playwright's 30 s in place; raise it for heavy lofts or a slow machine. |
Output Schema
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||