Creating EmDash plugins

Build against the API that reaches the intended execution mode. Source types and production-boundary tests take precedence over examples in this skill when they disagree.

Choose a format

Use a sandboxed plugin unless the feature needs host-process access, React admin code, Astro rendering components, raw page fragments, or custom Portable Text block definitions. Native plugins run with the site's authority and cannot be installed from the registry.

Scaffold a sandboxed plugin

pnpm dlx @emdash-cms/plugin-cli init my-plugin
cd my-plugin
pnpm install
pnpm run test

The manifest is the identity and trust contract. Runtime hooks and routes live in src/plugin.ts; the CLI generates descriptors, manifests, and bundles. Do not create a separate descriptor factory or sandbox-entry.ts.

import type { SandboxedPlugin } from "emdash/plugin";

const plugin: SandboxedPlugin = {
	hooks: {
		"content:afterSave": async (event, ctx) => {
			ctx.log.info("Content saved", { id: event.content.id });
		},
	},
};

export default plugin;

Import authoring types from emdash/plugin with import type. The CLI bundles value imports such as pluginRoute() and pluginResponse() from emdash/plugin and portableTextToMarkdown() from emdash/client. Sandboxed runtime code can use Web APIs but not Node.js built-ins.

Declare access

Declare every host API in emdash-plugin.jsonc. Adding authority, exposing a route publicly, or adding MCP tools requires renewed administrator approval.

Settings, KV, declared storage, logging, and cron scheduling are plugin-scoped and need no capability. Use ctx.settings for user configuration, ctx.kv for internal key-value state, and declared ctx.storage.<collection> for queryable records.

Read the focused reference for the API being used:

• Content, schema, translations, and publication
• Taxonomies and redirects
• Comments
• Media
• Storage, KV, and encrypted settings

Routes, HTTP, and MCP

Routes are private by default and require authentication, their declared RBAC permission, token scope or CSRF as appropriate. Public routes are internet-facing and require explicit install consent.

Undeclared routes keep the legacy JSON/query envelope. Declare methods and body modes for host-enforced parsing. Use pluginResponse() only on a route that declares a raw response. Outbound ctx.http.fetch() responses and declared route bodies are buffered and bounded.

MCP tools reference private JSON routes with explicit permissions and Zod input schemas. Mark difficult-to-reverse operations destructive: true. Read API routes and MCP tools.

Hooks

Sandboxed hooks enter the same priority, dependency, timeout, error-policy, enablement, exclusive-provider, and capability pipeline as trusted hooks. Publication policy hooks identify action origin and actor without granting publication authority. Comment moderation invoked through ctx.comments reports plugin origin and runs the normal after-hook once. Read Hooks.

Declarative admin UI

Sandboxed pages and widgets return validated Block Kit. Structured links use host-resolved targets; routeCtx.ui carries host-attested locale, direction, and surface. External images require matching network authority.

Saved-entry panels and actions point to private routes. Ordinary panel load receives only host-reloaded saved identity and version. Add admin.editor-draft:read or admin.editor-draft:patch plus extension-level collection and field selectors when an explicit interaction must receive selected unsaved fields or propose an atomic whole-field patch. Patch does not imply read. The host previews accepted patches, marks the form dirty, and never saves them automatically. Read saved content through capability-gated ctx.content.

Declarative field widgets currently compose supported Block Kit elements into a JSON value. Custom Portable Text blocks and Astro render components remain native-only. Read Admin UI, Block Kit, and Portable Text blocks.

Runner parity

Cloudflare Worker Loader and Node/workerd execute the same bundle behind a plugin-scoped bridge. Both return buffered WHATWG responses from ctx.http.fetch() with binary bytes preserved and decoded request/response bodies limited to 8 MiB. Write against exported types, not extra methods found in one wrapper.

Read Sandbox boundaries before designing around an API not listed here.

Test the production boundary

Use createPluginTestHost() for fast hook, route, manifest, capability, KV, settings, and storage transport tests. Use createPluginRuntimeTestHost() when the test must exercise real content actions, plugin activation, media, comments, redirects, scheduling, restart, authorization, CSRF, caching, Block Kit validation, or saved-entry extensions.

Runtime fixtures establish state without firing hooks. Runtime actions call production boundaries; inspectors read observable state. Queue outbound HTTP responses with host.http.respond() and inspect requests with host.http.requests(). Dispose every host after use. Add Node/workerd parity only for runner-sensitive behavior.

References

• Content, schema, translations, and publication
• Taxonomies and redirects
• Comments
• Media
• Hooks
• Storage, KV, and encrypted settings
• Admin UI and field widgets
• API routes and MCP tools
• Block Kit
• Portable Text blocks
• Sandbox boundaries
• Publishing