# 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](/docs/build/hosted-text), [hosted speech](/docs/build/hosted-speech), [hosted music and sound effects](/docs/build/hosted-music), [hosted images](/docs/build/hosted-images), or [image description](/docs/build/image-description) for those specific reviewed requests. Accepted project speech can be [added to Editor audio](/docs/build/audio-to-editor) 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](/docs/build/comfyui) 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](/docs/build/javascript), [media](/docs/build/media), and [automation](/docs/project-types/automation) for the additional host limits.