Runtime capabilities
Choose an implementation supported by SDK 0.1.0.
Supported execution
| Capability | SDK 0.1.0 |
|---|---|
| Declarative recipes | Supported; bounded allowlisted operations |
| Standalone JavaScript | Supported in isolated QuickJS |
| Hosted text.generate | Exact model, account BYOK or credits, and explicit run review |
| Hosted audio.speech | One short text/script input to measured audio in any StillMade catalog voice (Deepgram, ElevenLabs, OpenAI, Kokoro) with credits, or OpenAI with your key; playback review; accepted project recordings can be explicitly added to Editor audio |
| Hosted audio.transcribe | One owner-scoped stored audio asset to reviewed text and ordered word timings with StillMade transcription on credits, or OpenAI Whisper with your key |
| Hosted audio.music | One prompt to generated music (5–240 seconds) with StillMade credits and playback review |
| Hosted audio.sfx | One prompt to a generated sound effect (0.5–22 seconds) with StillMade credits and playback review |
| Hosted image.generate | One prompt and optional reference images to a stored PNG with any catalog image model and its settings; StillMade credits or account key, and actual image review |
| Hosted video.generate | One prompt and optional first/last frames to a measured stored video clip with any catalog video model and its settings; StillMade credits and actual video review |
| Hosted image.describe | One to four owned images to bounded production notes; host-selected model/payment and actual description review |
| Hosted media.analyze | One owned video (optionally one time range), image or up to four images to structured visual evidence: summary, timeline, observations, on-screen text and issues, with StillMade credits |
| Hosted web.fetch | One public web page read by the host and answered against the Block's instruction, with StillMade credits; no cookies, keys or private addresses |
| Hosted web.research | One topic searched on the web and summarized with cited sources, with StillMade credits |
| Hosted timeline.propose | Bounded typed context to strict timeline-edit JSON; host-selected model/payment, stale-before checks, preview and Apply |
| Hosted workspace.propose | Bounded typed context to a strict workspace-edit proposal for one permitted workspace; preview and explicit Apply |
| Hosted connection.execute | One reviewed action on a connected third-party app account through the host connection service; the Block never receives account credentials |
| Typed inputs, outputs, semantic roles | Supported |
| Schema-driven controls | Supported |
| Scoped project context snapshots | Supported in Step workspaces |
| Conditional SDK Steps | Supported with a compatible pass-through output |
| Current-media batches | Supported for saved Canvas, panel/board, voiceover and editor media |
| Future saved media | Supported with owner confirmation and the configured host worker |
| Host editor and generation tools | Existing built-in Blocks; normal host controls and permissions |
| Python, npm dependencies, shell, arbitrary native code | Not exposed to external packages |
| Package-supplied React workspace UI | Not exposed |
| Direct guest network, filesystem, or secrets | Not exposed |
| ComfyUI execution adapter | Reviewed core image nodes with explicit account connection and remote tests |
| Marketplace payments and seller onboarding | Not available; Blocks and Project Types are free |
Choose the boundary
Implement deterministic text or pixel transformations with recipes or JavaScript. Use hosted text, hosted speech, hosted music and sound effects, hosted images, or image description for those specific reviewed requests. Accepted project speech can be added to Editor audio through the host controls. Native Voiceover master recordings, takes, transcripts, and its primary script input retain their existing behavior. A runtime label or permission declaration does not create an unavailable host API.
ComfyUI and external backends
The Block contract is independent of the execution backend. The reviewed adapter runs bounded core-image workflows using an explicit account connection. It supports reviewed core image generation using an already-installed safetensors checkpoint. It cannot install dependencies or run custom Python nodes. See ComfyUI Blocks for package structure, fixture expectations, import review and current limits. Imported source is never loaded as host code.
Environment differences
The same portable Block can run in web, macOS, and Windows hosts. Desktop media and export features belong to the host capability bridge; a guest still receives bounded input data and no unrestricted disk access.
Limits
JavaScript runs have a 500 ms guest deadline, 16 MiB heap, 512 KiB stack, 256 KiB source ceiling, and 4 MiB serialized input/output budgets. Recipes permit at most 64 operations. See JavaScript, media, and automation for the additional host limits.