Plugin Overview

What is a Plugin?

A Plugin defines a custom message type. It controls:

What data a message carries via an input schema (what fields the agent sends)
How that message renders as HTML/CSS/JS in a sandboxed iframe
What logic runs client-side such as HTTP requests, data fetching, user interactions
What configuration it needs like environment variables (API keys, URLs, etc.)

A Plugin does NOT control:

Whether a message requires a review/response (that’s the agent’s decision per message)
The approve/reject buttons (that’s the review system, orthogonal to plugins)
Authentication or routing (that’s the platform)

Plugin vs Review

These are two independent axes on a message:

Message
  ├── metadata.plugin: "form-submit"    ← HOW the message renders (Plugin)
  ├── review: { ... }                   ← WHETHER user input is needed (Review)
  │     ├── type: "approval"            ← WHAT kind of input
  │     └── payload: { options: [...] }
  └── metadata: { name: "John", ... }   ← Plugin-specific data

Plugin Structure

Each plugin lives in packages/plugins/<name>/ and consists of:

plugin.json: Manifest with metadata, input schema, env variables, and permissions
render.html: HTML + CSS + JS rendered inside a sandboxed iframe
icon.svg/.png (optional): Icon shown in the Settings UI

Plugins are discovered automatically on backend startup. No build step required, just add the directory and restart.

Built-in Plugins

Placet ships with two example plugins you can use as reference:

Plugin	Description	Source
Form Submit	Renders a form from structured data and submits it to a configurable webhook URL	`packages/plugins/form-submit/`
Kroki Diagram	Renders diagrams (Mermaid, PlantUML, D2, etc.) via a Kroki server	`packages/plugins/kroki-diagram/`

Data Flow

Security Model

Concern	Solution
DOM access	`sandbox="allow-scripts"` only, no `allow-same-origin`, no parent DOM access
Cookies/Storage	Sandboxed iframe has no access to parent cookies or localStorage
HTTP requests	Server-side proxied; domain allowlist enforced via `maxHttpDomains`
Script injection	Plugin HTML is static per-plugin, loaded from disk
Env values	Stored in DB, injected at render time; secrets not exposed in manifest

Available in Plugins

Inside the iframe, plugins access the Bridge API via the Placet global:

Property	Type	Description
`Placet.data`	`Record<string, unknown>`	Plugin input data from the message metadata
`Placet.env`	`Record<string, string>`	Environment variables configured in Settings
`Placet.attachments`	`AttachmentInfo[]`	Array of attached files (`{ id, filename, mimeType, size }`)
`Placet.message`	`MessageContext`	Message context (`id`, `channelId`, `senderType`, `createdAt`)
`Placet.theme`	`'light' \| 'dark'`	Current theme
`Placet.review`	`ReviewContext \| null`	Review context (`{ type, status, payload }`) or `null`
`Placet.isPreview`	`boolean`	`true` when rendered in the full-screen preview modal

Methods: Placet.fetch(), Placet.getFile(), Placet.getFileUrl(), Placet.toast(), Placet.respond(), Placet.resize(), Placet.emit(), Placet.on(). See the full Bridge API reference for details.

Getting Started

Core Concepts

Connections

Examples

Plugins

Plugin Overview

What is a Plugin?

Plugin vs Review

Plugin Structure

Built-in Plugins

Data Flow

Security Model

Available in Plugins

​What is a Plugin?

​Plugin vs Review

​Plugin Structure

​Built-in Plugins

​Data Flow

​Security Model

​Available in Plugins

What is a Plugin?

Plugin vs Review

Plugin Structure

Built-in Plugins

Data Flow

Security Model

Available in Plugins