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languages](/docs/framework/site/i18n/)[Images](/docs/framework/site/images/)[Redirects](/docs/framework/site/redirects/)[Feeds](/docs/framework/site/feeds/)[Site search](/docs/framework/site/search/)[Build output and adapters](/docs/framework/site/deployment/)How compilation works[Overview](/docs/framework/build/)[The dev server](/docs/framework/build/dev-server/)[CLI commands](/docs/framework/build/cli/)Working with agents[Overview](/docs/framework/agents/)[Authoring rules for agents](/docs/framework/agents/authoring-rules/)[Machine-readable docs](/docs/framework/agents/machine-readable/)Reference[Overview](/docs/framework/reference/)[Formula catalog](/docs/framework/reference/formulas/)[Operator reference](/docs/framework/reference/operators/)Extending[Overview](/docs/extending/)Extensions[Extension anatomy](/docs/extending/extensions/anatomy/)[Schema composition](/docs/extending/extensions/schema-composition/)[Custom classes](/docs/extending/extensions/classes/)[Custom formats](/docs/extending/extensions/formats/)[Capability methods](/docs/extending/extensions/capabilities/)[Project sections](/docs/extending/extensions/project-sections/)[Server mounts](/docs/extending/extensions/server/)[Connectors](/docs/extending/extensions/connectors/)[Search indexes](/docs/extending/extensions/search/)[Security and secrets](/docs/extending/extensions/security/)[Tutorial: a TOML format](/docs/extending/extensions/tutorial-toml-format/)[Tutorial: a guestbook](/docs/extending/extensions/tutorial-guestbook/)[First-party extensions](/docs/extending/extensions/first-party/)Embedding[Overview](/docs/extending/embedding/)[Hosting the Studio assets](/docs/extending/embedding/hosting/)[Writing a platform adapter](/docs/extending/embedding/platform-adapter/)[The backend protocol](/docs/extending/embedding/backend-protocol/)[Dev server internals](/docs/extending/embedding/dev-server/)[Embedding the runtime in your app](/docs/extending/embedding/runtime-host/)[Writing assistant tools](/docs/extending/embedding/assistant-harness/)UI kit[The Jx UI kit](/docs/extending/ui-kit/)Reference[Protocol routes](/docs/extending/reference/studio-routes/)[Implementation status](/docs/extending/reference/implementation-status/)[Spec changelog](/docs/extending/reference/spec-changelog/)[Standards alignment](/docs/extending/reference/standards/)Contributing[Working in the monorepo](/docs/extending/contributing/monorepo/)[Contributing to these docs](/docs/extending/contributing/docs/)[AI assistant evals](/docs/extending/contributing/ai-evals/) # Capability methods Capabilities are how a class's declarations turn into behavior. They are declared in the descriptor's `$defs.methods` using well-known `role` values, and they are all `scope: "static"`, so hosts call them on the implementation class without constructing an instance. The instance `resolve()` method remains the runtime's on-demand access path; capabilities serve the build, the servers, and Studio. ## The contract A capability declaration is an ordinary method entry with a reserved `role`. The parser's `Content` class declares its `$paths` expansion capability like this (abbreviated): ```json shiki ``` To find and invoke a capability, a host scans `$defs.methods` for the `role`, takes the method's `identifier` (fallback: its key) as the static method name, imports `$implementation`, and calls `Export[identifier](...args)`. So the declaration above is fulfilled by `Content.resolvePaths(pathsDef, ctx)` in `content-loader.ts`: a plain exported static method, no framework API to implement. ## The roles | Role | Block | Signature | Consumers | | ---------------- | ----------- | ----------------------------------------------------------------------------------------------------- | ----------------------------------------------------------- | | `parse` | `format` | `(source, options?) → JxDocument` | compiler, server, Studio (open file) | | `serialize` | `format` | `(doc, options?) → string` | Studio (save), site build (export sidecars) | | `discover` | `format` | `(source, { baseDir }) → string[]` | content loading (list entry files) | | `load` | `format` | `(path, { schema, directiveOptions }) → ContentLoaderEntry[]` | content loading (parse one source) | | `projectData` | `project` | `(sectionValue, { projectConfig, root, registry, io, lazy? }) → unknown` | site build, dev server (result stored as `_project[]`) | | `resolvePaths` | `project` | `(pathsDef, { data, projectConfig, root, urlPattern, params, patterns }) → Record[]` | pages discovery (`$paths` expansion), Studio preview | | `lower` | any | `(def, context) → JxStateDefinition` | compiler (rewrites a state def into a core shape) | | `emit` | `project` | `(sectionValue, { projectConfig, root, sections, routes }) → EmitFile[]` | site build (writes derived assets into the build output) | | `assets` | `project` | `(sectionValue, { projectConfig, root }) → AssetMount[]` | site build, dev server (publishes directories at site URLs) | | `mount` | `server` | `(options, ctx) → (request, env) => Promise` | generated site worker, dev server | | `dialect` | `connector` | `(connection, env) → Kysely Dialect` | data mounts, auth, deploy | | `deploySchema` | `connector` | `(tables, connection, { env, dryRun }) → { statements, applied, warnings }` | `jx db push`, Studio push | | `bindings` | `connector` | `(connection) → wrangler config fragment` | scaffolding, `jx db push` | | `testConnection` | `connector` | `(connection, env) → { ok, error? }` | Studio connections UI, CLI | `resolvePaths` methods additionally declare a `discriminator`, the `$paths` key that routes to them. The parser's is `contentType`, so a page with `"$paths": { "contentType": "blog" }` dispatches to `Content.resolvePaths`. Hosts dispatch purely on which discriminator key is present in the `$paths` value; two extensions can coexist without either knowing the other's shape. The format roles are covered in depth in [Custom formats](/docs/extending/extensions/formats); the project roles in [Project sections and settings](/docs/extending/extensions/project-sections); `mount`, `dialect`, `deploySchema`, `bindings`, and `testConnection` in [Server mounts](/docs/extending/extensions/server) and [Connectors](/docs/extending/extensions/connectors). ## `timing` Each capability may declare a `timing` array, the environments allowed to invoke it directly: - Values: `"compiler"`, `"server"`, `"client"`. Default when omitted: `["compiler", "server"]` (assume node-only). - A host whose environment is excluded round-trips through the dev server (`POST /__studio/format`, `POST /__jx_resolve__`) instead of importing the implementation. - Capabilities that are browser-safe (no `fs`, `glob`, or node imports anywhere on their code path) should declare `"client"` so Studio can call them in-process. `Markdown.parse` declares all three, which is why typing in Studio's Markdown editor never touches the network; `Markdown.discover` reads the filesystem, so it stays `["compiler", "server"]`. Tip `timing` is per-method, not per-class. Mixed classes are normal: declare `"client"` on the pure-string transforms and let the filesystem-touching ones delegate. ## Options as parameters Capability options are declared as ordinary `parameters` with JSON-Schema types. There is no separate options vocabulary. `Markdown.serialize` declares its second parameter as: ```json shiki ``` Because the types, enums, and defaults are right there in the descriptor, Studio can render an options UI for any extension's capability without host-side knowledge of the extension: an enum becomes a picker, a boolean a toggle, a default the initial value. ## `lower` `lower` lets a state class compile away. At build time, when a state entry's [timing](/docs/framework/concepts/timing) excludes the compiler, the compiler checks the class descriptor for a `lower` capability and, if present, replaces the def in place with the returned core-shape def (`Request`, `Function`, …). The connector's `TableQuery` declares: ```json shiki ``` A page authored with `{ "$prototype": "TableQuery", "table": "posts", "timing": "client" }` compiles into a plain reactive fetch of `/_jx/data/posts?…`. Dynamic-data queries work in compiled sites with **no extension code shipped to the browser**. `lower` may appear on a class with any admission block (or none). ## `assets` `assets` publishes a directory your section already reads from at a site URL, so the files beside its sources are reachable: ```json shiki ``` Each returned pair is an **asset mount**: `{ "urlPrefix": "/content/blog", "dir": "/abs/path/to/content/blog" }`. The parser returns one per content type with a directory source, which is what lets a Markdown entry reference `./images/hero.png` and still resolve everywhere. A mount may also carry a `filter(path)`, asked with a file's path relative to `dir`, that says whether the mount serves it. The parser sets one on a content type that declares `exclude`, `where` or `route`, so an excluded folder, a hidden file or a Markdown document is never reachable through the mount, however a page names it. Hosts get this for free through `assetUrlFor` and `resolveAssetUrl`. A filter is a function, so it exists where the mount was declared and does not survive a serialized copy. Hosts do three things with a mount, and your extension writes none of them: - the site build resolves mounted URLs for [image optimization](/docs/framework/site/images), then copies **only the files the compiled output references** to their URL path in `dist/`; - the dev and desktop servers serve the mount ahead of the project root, so previews match the built site; - `jx preview` needs nothing, because it serves `dist/`, where the files already are. `dir` may sit outside the project root. That is the point. Return the mount from the section's config alone: the call is expected to be cheap and side-effect-free, and hosts may make it per request. A `urlPrefix` claimed for two different directories is a configuration error; sharing one `dir` across prefixes is fine. ## Related - [Custom classes](/docs/extending/extensions/classes): the descriptors capabilities live in - [Custom formats](/docs/extending/extensions/formats): the four format roles in context - [Project sections and settings](/docs/extending/extensions/project-sections): `projectData` and `resolvePaths` in context - [Timing](/docs/framework/concepts/timing): the state-entry timing model `lower` keys off ✕ Start here[Overview](/docs/start/)Get started[Install Jx Studio](/docs/start/install/)[Your first project](/docs/start/first-project/)[A tour of Jx Studio](/docs/start/studio-tour/)Tutorials[Tutorial: interactive component](/docs/start/first-component/)[Tutorial: blog with collections](/docs/start/first-collection/)[Video tutorials](/docs/start/videos/)Coming from another tool[Coming from WordPress](/docs/start/coming-from-wordpress/)[Coming from Webflow or Framer](/docs/start/coming-from-webflow/)[Coming from Wix or Squarespace](/docs/start/coming-from-wix/)[Coming from Lovable or Builder.io](/docs/start/coming-from-ai-builders/)Studio[Overview](/docs/studio/)[The desktop app](/docs/studio/desktop/)The workspace[Overview](/docs/studio/interface/)[Welcome screen](/docs/studio/interface/welcome-screen/)[Editors and views](/docs/studio/interface/modes/)[The canvas](/docs/studio/interface/canvas/)[Documents and panes](/docs/studio/interface/tabs/)[Quick Access](/docs/studio/interface/quick-access/)[Keyboard shortcuts](/docs/studio/interface/shortcuts/)[Preferences](/docs/studio/interface/preferences/)[Languages](/docs/studio/interface/languages/)[Problems and progress](/docs/studio/interface/problems-and-progress/)[Commands](/docs/studio/interface/commands/)Projects[Overview](/docs/studio/projects/)[Create a project](/docs/studio/projects/create/)[Pages, layouts, components](/docs/studio/projects/pages-layouts-components/)[The Content workspace](/docs/studio/projects/browse/)[Starter templates](/docs/studio/projects/starters/)[Media](/docs/studio/projects/media/)[Content types](/docs/studio/projects/content-types/)[Project settings](/docs/studio/projects/settings/)[Dependencies and imports](/docs/studio/projects/dependencies/)Edit mode[Overview](/docs/studio/editing/)[Writing and formatting](/docs/studio/editing/writing/)[Slash commands](/docs/studio/editing/slash-commands/)[Frontmatter and metadata](/docs/studio/editing/frontmatter/)[Grid mode](/docs/studio/editing/grid/)Design mode[Overview](/docs/studio/design/)[Outline](/docs/studio/design/layers/)[Insert](/docs/studio/design/elements/)[Content tab](/docs/studio/design/properties/)[Style inspector](/docs/studio/design/style-inspector/)[Breakpoints](/docs/studio/design/breakpoints/)[States and selectors](/docs/studio/design/states-and-selectors/)[Design tokens](/docs/studio/design/tokens/)[Project Styles](/docs/studio/design/stylebook/)[Working with 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prototypes](/docs/framework/concepts/data-prototypes/)[Timing](/docs/framework/concepts/timing/)[Dynamic switching](/docs/framework/concepts/switching/)[Security](/docs/framework/concepts/security/)Site architecture[Overview](/docs/framework/site/)[project.json](/docs/framework/site/project-json/)[Routing](/docs/framework/site/routing/)[Layouts](/docs/framework/site/layouts/)[Content collections](/docs/framework/site/content-collections/)[Jx Markdown](/docs/framework/site/jx-markdown/)[Obsidian vault as content](/docs/framework/site/obsidian-vault/)[Relationships](/docs/framework/site/relationships/)[SEO and metadata](/docs/framework/site/seo/)[Locales and languages](/docs/framework/site/i18n/)[Images](/docs/framework/site/images/)[Redirects](/docs/framework/site/redirects/)[Feeds](/docs/framework/site/feeds/)[Site search](/docs/framework/site/search/)[Build output and adapters](/docs/framework/site/deployment/)How compilation works[Overview](/docs/framework/build/)[The dev server](/docs/framework/build/dev-server/)[CLI commands](/docs/framework/build/cli/)Working with agents[Overview](/docs/framework/agents/)[Authoring rules for agents](/docs/framework/agents/authoring-rules/)[Machine-readable docs](/docs/framework/agents/machine-readable/)Reference[Overview](/docs/framework/reference/)[Formula catalog](/docs/framework/reference/formulas/)[Operator reference](/docs/framework/reference/operators/)Extending[Overview](/docs/extending/)Extensions[Extension anatomy](/docs/extending/extensions/anatomy/)[Schema composition](/docs/extending/extensions/schema-composition/)[Custom classes](/docs/extending/extensions/classes/)[Custom formats](/docs/extending/extensions/formats/)[Capability methods](/docs/extending/extensions/capabilities/)[Project sections](/docs/extending/extensions/project-sections/)[Server mounts](/docs/extending/extensions/server/)[Connectors](/docs/extending/extensions/connectors/)[Search indexes](/docs/extending/extensions/search/)[Security and secrets](/docs/extending/extensions/security/)[Tutorial: a TOML format](/docs/extending/extensions/tutorial-toml-format/)[Tutorial: a guestbook](/docs/extending/extensions/tutorial-guestbook/)[First-party extensions](/docs/extending/extensions/first-party/)Embedding[Overview](/docs/extending/embedding/)[Hosting the Studio assets](/docs/extending/embedding/hosting/)[Writing a platform adapter](/docs/extending/embedding/platform-adapter/)[The backend protocol](/docs/extending/embedding/backend-protocol/)[Dev server internals](/docs/extending/embedding/dev-server/)[Embedding the runtime in your app](/docs/extending/embedding/runtime-host/)[Writing assistant tools](/docs/extending/embedding/assistant-harness/)UI kit[The Jx UI kit](/docs/extending/ui-kit/)Reference[Protocol routes](/docs/extending/reference/studio-routes/)[Implementation status](/docs/extending/reference/implementation-status/)[Spec changelog](/docs/extending/reference/spec-changelog/)[Standards alignment](/docs/extending/reference/standards/)Contributing[Working in the monorepo](/docs/extending/contributing/monorepo/)[Contributing to these docs](/docs/extending/contributing/docs/)[AI assistant evals](/docs/extending/contributing/ai-evals/) [![Jx Suite](/favicon.svg) Suite](/)The visual IDE for the web. 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