---
name: formio-form
description: >-
  Embed and render Form.io forms in any web application with the Vanilla JS renderer `@formio/js` — render by URL or JSON, pre-fill with submissions, JavaScript control, renderer options, conditional fields, calculated values, JSON Logic validation, cascading selects, and conditional wizard pages. The library's default "embed a form" entry point. Use when the user asks to "embed a form", "render a form", "add this form to my page/site/app", "pre-fill a form", "show or hide a field based on another field", "calculate a field value", or "add custom validation to a field" — field behavior inside ANY framework's rendered form stays here. Not for: scaffolding or configuring an Angular app with `@formio/angular` (see `formio-angular`); building an app around data (see `formio-application`); designing the data model (see `formio-resource-planner`); REST endpoints (see `formio-api`); the raw SDK/Utils API reference (see `formio-sdk`); creating a NEW form — embed-only skill (see `formio-form-builder`).
---

# Embedding Form.io Forms (Vanilla JS renderer)

Task guide for putting a Form.io form on a page and wiring its behavior with the `@formio/js` renderer. Everything routes through one API:

```js
const form = await Formio.createForm(element, srcOrJson, options);
```

## Preflight — the Form.io MCP server

**Check this when you reach your first Form.io tool call, not when this skill activates.** The check is whether `form_list`, `form_create`, `project_import`, `project_set`, `project_get` are callable by you. A Form.io-branded MCP server that does not expose them is not this server — an entry named for Form.io offering only connection or authentication tools does not satisfy this check, and "installed but not authenticated" is not a state this design has or that you may report. Either those tools are there or they are not.

**A missing server blocks that call, not the turn.** Reading this skill, answering a question from it, planning, and writing files to the working directory all need no server. Do everything that needs no server first and in full, then raise the gap when you actually reach the call that needs it. Opening with a blocked-on-setup message — or asking for a Project URL before there is anything to write to it — spends the user's turn on a step that was not due.

When you do reach that call and the tools are missing, stop there and load the `formio-mcp-setup` skill; it writes the MCP configuration this client reads, offers to capture the project configuration, and tells the user how to reload. This skill writes no MCP configuration itself, and **that skill is the only remedy you offer.** Do not invent one: no client menu, no slash command, no "authorize in the browser", no install or reload steps of your own. The setup skill owns every instruction the user receives, and an invented one sends them looking for a server entry that nothing ever wrote. If `formio-mcp-setup` is not installed either, tell the user:

> I have no Form.io tools, so the Form.io MCP server is not connected, and the `formio-mcp-setup` skill that would connect it is not installed either. Both ship in the Form.io skill library at https://github.com/formio/ai — its README carries the install route for every client, including the MCP server entry to add if you would rather configure it directly.

**Never pre-announce authentication.** Authentication is implicit: the first authenticated tool call opens the portal-login flow itself when no cached JWT is present. There is no authenticate-first step to ask the user for, and no unauthenticated state to diagnose before a call has actually failed.

Do **not** work around missing tools by making direct HTTP requests against a Form.io deployment, and do not write a throwaway script that makes them for you. This library documents the whole Form.io REST surface, which makes hand-rolling requests tempting and wrong — it bypasses the guardrails the tools enforce and can write to a live deployment unreviewed. Stop and report what is blocking instead.

That ban is on **build-time** work — the configuring you do in this session. It says nothing about the application you are building: an app is expected to call the Form.io REST API **at runtime**, to log its users in and to read and write their submissions, and [`formio-api`](../formio-api/SKILL.md)'s runtime-scope references document those endpoints for exactly that code.

**Available tools are not a configured project.** Every Form.io tool resolves which project it targets per working directory, so pass `cwd` — the user's current working directory — on every Form.io tool call; omitting it resolves against the MCP server's own directory, which is fixed at spawn and may be mapped to a different project. Before the first call that reads from or writes to a deployment, ask the server what this directory resolves to by calling the `project_get` tool with `cwd` set to the user's current working directory. Do not shell out for this: the connected server answers it directly, with the same resolver every other tool uses, so what it reports is what the next call targets.

What `project_get` returns IS the configuration. There is one value to think about — the **Project URL**, the full URL of the Form.io project this work reads and writes. The **Base URL** (the deployment hosting it) is normally DERIVED from that project URL rather than supplied, so it is not a second thing to ask for. The values may come from a committed `formio.json` tracked with the application's own source, from this directory's mapping, or from the environment — the report says which. Do not ask the user to confirm or re-supply either one.

Branch on the `status` it returns. On `ok`, proceed. On `not-configured` — nothing is recorded for this directory — relay that message's own instruction to the user, ask for the single value it names, record it with `project_set`, and call `project_get` again. On `base-url-unresolved` the project IS recorded and one named value is still missing — the Base URL, for a project URL that names no deployment of its own: relay that message the same way, ask the user for that one value, and do exactly what that message names — which record the deployment goes in decides what the fix IS, and the report names it rather than leaving you to compose one. For a project this directory's own mapping holds, that is a `project_set` call, and the report also carries it as a structured `remedy`. For a project a committed `formio.json` holds, it is an EDIT to that file — the report names the path and the key, there is no `remedy` field to act on, and this server never writes a committed file, so composing a `project_set` call there is refused. Then call `project_get` again. Do not re-ask the user for the Project URL there; the report already reported it, and the call it names carries it for you. If the call fails outright instead of returning a status, it could not answer at all (an unreadable `~/.formio/projects.json`, a `formio.json` that will not parse, a malformed URL): do NOT interview, because a `project_set` would fail for the same unreported reason and the loop would repeat with the cause never named — relay the error and stop until it is fixed. Before the first call that WRITES (`form_create`, `form_update`, `role_create`, `action_create`, `project_import`), state the resolved Project URL and Base URL in one line, so a wrong target is caught before anything is written to it.

Never invent a Base URL, never reuse one from another project or an earlier session, and never edit `~/.formio/projects.json` by any means — its shape, its `0600` mode, and its merge rules belong to the server, and `project_set` is how you reach it. The server's own messages carry the URL shapes and the remedy for each; this skill does not restate them.

## How to navigate this skill

Read the reference that matches the task; each is self-contained and states which behaviors compose with which.

| Task | Reference |
| --- | --- |
| Page prerequisites — CDN/ESM includes, target `<div>`, Hosted vs SaaS URLs | [references/setup.md](./references/setup.md) |
| Render a form by URL, by JSON, or with a submission (pre-fill) | [references/rendering.md](./references/rendering.md) |
| Control the form from JavaScript — events, submission data, components | [references/javascript-api.md](./references/javascript-api.md) |
| Renderer options (`readOnly`, `noAlerts`, `hooks`, `i18n`, `sanitizeConfig`, …) | [references/options.md](./references/options.md) |
| JSON Logic primer — operations and `var` resolution (`data`, `row`, `input`) | [references/json-logic.md](./references/json-logic.md) |
| Show/hide components conditionally (simple and JSON Logic) | [references/conditionals.md](./references/conditionals.md) |
| Compute a field from other fields (`calculateValue`) | [references/calculated-values.md](./references/calculated-values.md) |
| Custom validation rules (`validate.json`) | [references/validation.md](./references/validation.md) |
| Advanced field logic (`logic` triggers and actions) | [references/field-logic.md](./references/field-logic.md) |
| External data sources and cascading selects (make → model → year) | [references/external-data.md](./references/external-data.md) |
| Wizards — conditional pages, custom navigation | [references/wizards.md](./references/wizards.md) |

## Security — a form definition is executable code

A form definition is not inert data. `calculateValue`, `validate.custom`, `logic` actions, HTML/Content component bodies, and select `template` strings are all evaluated by the renderer at render time, in the page's own JavaScript context. Anything that can supply a form definition can therefore run code in your page. Four rules follow, and they apply to every reference in this skill:

- **Render only definitions from a project you control.** A form URL or JSON blob is a code-execution channel: never render a definition supplied by an end user, uploaded as a file, pasted into your app, or fetched from a third-party host. `Formio.setBaseUrl` / `Formio.setProjectUrl` must point at your own Form.io deployment.
- **`fetch.authenticate: true` sends the user's Form.io token.** On a Data Source component (and on select URLs) it attaches the current session's auth token to the outbound request, so pointing that URL at a host you do not own hands your users' credentials to that host. Enable it only for endpoints on your own deployment; for any third-party API leave it `false` and authenticate server-side instead. Same rule for `fetch.forwardHeaders`, which forwards the incoming request's headers verbatim.
- **Do not widen the HTML sanitizer to allow script execution.** The renderer sanitizes labels and HTML content through DOMPurify. `sanitizeConfig.addTags` / `addAttr` ([references/options.md](./references/options.md)) exist for markup like `<iframe>` or `target`; adding `script`, `on*` event attributes, or `srcdoc` turns component content into an XSS vector for anyone who can edit the form.
- **Submitted `data.*` is untrusted in the code you write around the form.** Embedding is build-time work; the values arrive at runtime, in the deployed app, from whoever fills the form in. Anywhere your own code puts a submitted value back into the page — a confirmation screen, a summary table, an `innerHTML`, a URL you build — escape it there, because the renderer's sanitizer covers what it renders and not what you render. The server-side half of the same rule (email bodies, webhook payloads, recipient lists) is in `formio-actions`.

## When the form does not exist yet

This skill embeds forms that already exist. If the embed request reveals the form is not in the user's project yet (`form_get` misses, or the user is describing a form from scratch — "embed a multi-step intake wizard on my page"), route to `formio-form-builder` first: it determines the form type (webform vs wizard vs PDF form), authors the definition, and saves it. When it finishes, embedding resumes here with the saved form URL.

## URL terminology

- `baseUrl` refers only to the **Base URL** — the deployment hosting the project.
- `projectUrl` refers only to the **Project URL** — the project this work reads and writes, and the one value anyone supplies.

Both are values `project_get` reports, not variables to read: nothing looks them up in the environment. Neither is composed from the other, and the shapes each one takes on each kind of deployment are in [`project-urls.md`](../formio-mcp-setup/references/project-urls.md) rather than here — one copy, so the two cannot drift apart.

Form URLs passed to `Formio.createForm` live under the project URL: `{projectUrl}/{formPath}`. See [references/setup.md](./references/setup.md) for configuring both.

## MCP Tool Preference

When an embed task requires reading or changing the form definition itself, prefer the MCP server's first-party tools over ad-hoc HTTP requests:

- `form_get` / `form_list` — fetch the form JSON you are about to render or inspect its components.
- `form_update` / `form_create` — persist component changes (conditionals, `calculateValue`, `validate.json`, `logic`) back to the project. The server authenticates implicitly via its browser-based portal-login flow: the first authenticated tool call triggers it on a cache miss, captures a portal JWT, and attaches it to every request as the `x-jwt-token` header via `formioFetch`. There is no explicit authenticate tool. Do not use PKCE or API keys.