plasmic-designer - SKILL.md Agent Skill

name: plasmic-designer description: Build and modify Plasmic Studio designs using copilot tools via Chrome DevTools MCP. First argument should be a project ID, followed by the design request. Use this skill whenever the user mentions Plasmic, Plasmic Studio, visual web builder, or asks to design, build, edit, or modify UI components, pages, sections, or layouts inside a Plasmic project. Also trigger when the user references a Plasmic project ID, wants to add/remove/restyle elements in a visual editor, or asks about Plasmic component props, variants, slots, or tokens — even if they don't say "Plasmic" explicitly but describe visual design work that implies it. allowed-tools: mcpchrome-devtoolsevaluate_script mcpchrome-devtoolsnavigate_page mcpchrome-devtoolstake_screenshot mcpchrome-devtoolslist_pages metadata: version: "1.1.0"

Plasmic Designer

Skill Version: 1.1.0

Control Plasmic Studio through Chrome DevTools MCP to build and modify production-ready interfaces.

Arguments

$ARGUMENTS should contain a project ID as the first word, followed by the design request.

Example: /plasmic-designer j2Bm3mrbGNKsXVW3Wf5KpP Add a hero section to the Homepage

If no project ID is provided, or if the conversation references multiple projects and it's unclear which one to use, ask the user to confirm the project ID before proceeding.

Setup

The studio base URL is https://studio.plasmic.app by default. Only use http://localhost:3003 if the user explicitly mentions localhost, a local dev server, or a local environment.

Navigate to the project using navigate_page to open {baseUrl}/projects/{projectId}/
Wait for studio to load and identify the session — the studio takes a few seconds to initialize. Poll until window.PLASMIC_AI_TOOLS is available, then call identify() once, before any other tool.
```
async () => {
  for (let i = 0; i < 30; i++) {
    if (window.PLASMIC_AI_TOOLS) {
      return await window.PLASMIC_AI_TOOLS.identify({
        model: "<model>",
        client: "<client>",
        skill: "<skill>",
      });
    }
    await new Promise((r) => setTimeout(r, 1000));
  }
  return {
    success: false,
    error: { message: "Studio failed to load." },
  };
};
```
Fields (all required):
- model — Model name as known to the agent (e.g. claude-opus-4-7, anthropic/claude-sonnet-4-6, gpt-5.3-codex).
- client — AI client/CLI invoking the tool (e.g. claude-code, claude-code@1.x, opencode, cursor, cline).
- skill — Skill name and version being used (e.g. plasmic-designer@1.1.0, unknown).
Pass "unknown" for any field you cannot reliably identify.

If success is false, inform the user and stop.

Workflow

Follow an explore-first pattern for every request:

Understand — read the current state before changing anything; prefer reusing existing components over new HTML.
Plan — For complex requests, break the work into steps before acting.
Execute — Make changes with the appropriate tools.
Verify — read to confirm structural changes; Optionally, take_screenshot to confirm the result visually

Using the tools

The toolset is exposed at runtime and is the source of truth — introspect it, don't rely on a hardcoded list. _meta is a Record<string, CopilotToolMeta> keyed by tool name:

interface CopilotToolMeta {
  toolName: string;
  title: string;
  description: string;
  inputSchema: JSONSchema7; // JSON Schema (draft-07)
}

Read it once with evaluate_script (return the object directly; evaluate_script serializes it for you), and treat each tool's inputSchema as authoritative for field names, required fields, enums, and nesting:

() => window.PLASMIC_AI_TOOLS._meta;

Call a tool with an async arrow function (tools return Promises), passing one input object that conforms to its schema:

async () => await window.PLASMIC_AI_TOOLS.<toolName>({
  /* fields per window.PLASMIC_AI_TOOLS._meta.<toolName>.inputSchema */
});

Every call resolves to a CopilotToolCallResult:

type CopilotToolCallResult =
  | { success: true; output: string }
  | {
      success: false;
      error: { message: string; type: "TOOL_NOT_FOUND" | "EXECUTION_FAILED" };
    };

Check success each time; on a UUID error, re-read for fresh UUIDs and retry.

Call read before any mutation to get project structure and the UUIDs every other tool needs. Its output is usually XML: parse it for UUIDs, props, variants, and slots, and read selectively (specific components/elements) on large projects. After a successful mutation the canvas updates automatically.

Components & Variants

Targeting

Mutation tools require a componentUuid (from read results). They accept an optional variantUuids array — when omitted, changes apply to the base variant.

Reusing Existing Components

When you read a component, the output includes props (text, boolean, enum, number, href with defaults), variants (boolean toggles or enum option groups), slots (named content areas), base-variant-tpl-tree (element tree with styles), and VariantSettings (style overrides per variant). Review these to understand the component before using it.

To use a component in insertHtml:

<plasmic-component
  data-plasmic-component="ComponentName"
  data-plasmic-project="importedProjectId"
  data-plasmic-name="primaryCta"
  data-props='{"propName":"value","variantGroup":"optionName"}'
  style="margin: 16px;"
>
  <div slot="slotName">Slot content here</div>
</plasmic-component>

data-plasmic-component must exactly match the component name from read() (case-sensitive).
data-plasmic-project (optional) is the id of the imported project the component comes from. Omit it for components in the current project; set it to use a component from an imported project.
data-plasmic-name (optional) names this component instance in the tree. It's a semantic name picked up by Plasmic codegen to override the element in the generated code.
data-props is a JSON object for both props and variant activations. Boolean variants: "group": true. Enum variants: "group": "optionName".
slot="slotName" on direct children fills a named slot.
Only layout/position styles work on instances: width, height, min/max sizing, margin, position, top/left/bottom/right, z-index, order, align-self, flex-grow/shrink, opacity, display (only none), transform, and transition properties. Background, padding, color, font, border, etc. are ignored on instances — use changeElement on the component's root element instead. This is a Plasmic platform constraint, not a preference.

HTML Code Guidelines

Before generating HTML, read references/html-constraints.md for the full set of rules. The key points:

Use <style> blocks with BEM-style class names instead of inline styles.
Use flex layout exclusively (Plasmic does not support CSS Grid).
Include @media queries for responsive breakpoints — read the project's breakpoints (with screenBreakpoints) first.
Use Google Fonts (single name, no fallback lists).
Use inline SVG for icons, https://placehold.co for placeholder images.
No JavaScript, no vendor prefixes, no data:image/svg+xml, no currentColor, no :root.

Design Quality

Before generating designs, read references/design-guidelines.md for aesthetic principles and design thinking guidance.

Design Tokens

Read the project's tokens before generating designs, then:

Prefer existing tokens over hardcoded values for consistency. Reference them as var(--token-<uuid>).
If a token's value doesn't match the design intent, use a hardcoded value instead — design accuracy matters more than token reuse.
Not every value needs a token. Use them for deliberate design decisions (brand colors, type scale), not incidental one-off values.

Modifying Existing Components

Small changes (color, spacing) — apply directly with changeElement or insertHtml.
Significant changes to widely-used components — describe the proposed changes and ask the user before proceeding, since edits can cascade across the project.
Variant-scoped changes — when possible, scope changes to a specific variant to avoid breaking other usages.

Response Format

Be brief and action-oriented. Lead with what you did.
Summarize changes in 1-2 sentences.
Don't repeat the user's request or give lengthy explanations unless asked.