OpenWebUI Plugin Development Guide

This guide consolidates official documentation, SDK details, and best practices to provide a systematic tutorial for developers, from beginner to expert.

📚 Table of Contents

Quick Start
Core Concepts & SDK Details
Deep Dive into Plugin Types
- Action
- Filter
- Pipe
Advanced Development Patterns
Best Practices & Design Principles
Repository Standards (openwebui-extensions)
Custom Agent Design Recommendations
Troubleshooting

1. Quick Start

1.1 What are OpenWebUI Plugins?

OpenWebUI Plugins (officially called "Functions") are the primary way to extend the platform's capabilities. Running in a backend Python environment, they allow you to:

🔌 Integrate New Models: Connect to Claude, Gemini, or custom RAGs via Pipes.
🎨 Enhance Interaction: Add buttons (e.g., "Export", "Generate Chart") next to messages via Actions.
🔧 Intervene in Processes: modify data before requests or after responses (e.g., inject context, filter sensitive words) via Filters.

1.2 Your First Plugin (Hello World)

Save the following code as hello.py and upload it to the Functions panel in OpenWebUI:

"""
title: Hello World Action
author: Demo
version: 1.0.0
"""

from pydantic import BaseModel, Field
from typing import Optional

class Action:
    class Valves(BaseModel):
        greeting: str = Field(default="Hello", description="Greeting message")

    def __init__(self):
        self.valves = self.Valves()

    async def action(
        self,
        body: dict,
        __event_emitter__=None,
        __user__=None
    ) -> Optional[dict]:
        user_name = __user__.get("name", "Friend") if __user__ else "Friend"
        
        if __event_emitter__:
            await __event_emitter__({
                "type": "notification",
                "data": {"type": "success", "content": f"{self.valves.greeting}, {user_name}!"}
            })
        return body

2. Core Concepts & SDK Details

2.1 ⚠️ Important: Sync vs Async

OpenWebUI plugins run within an asyncio event loop.

Principle: All I/O operations (database, file, network) must be non-blocking.
Pitfall: Calling synchronous methods directly (e.g., time.sleep, requests.get) will freeze the entire server.
Solution: Wrap synchronous calls using await asyncio.to_thread(sync_func, ...).

2.2 Core Parameters

All plugin methods (inlet, outlet, pipe, action) support injecting the following special parameters:

Parameter	Type	Description
`body`	`dict`	Core Data. Contains request info like `messages`, `model`, `stream`.
`__user__`	`dict`	Current User. Contains `id`, `name`, `role`, `valves` (user config), etc.
`__metadata__`	`dict`	Metadata. Contains `chat_id`, `message_id`. The `variables` field holds preset variables like `{{USER_NAME}}`, `{{CURRENT_TIME}}`.
`__request__`	`Request`	FastAPI Request Object. Access `app.state` for cross-plugin communication.
`__event_emitter__`	`func`	One-way Notification. Used to send Toast notifications or status bar updates.
`__event_call__`	`func`	Two-way Interaction. Used to execute JS code, show confirmation dialogs, or input boxes on the frontend.

2.3 Configuration System (Valves)

Valves: Global admin configuration.
UserValves: User-level configuration (higher priority, overrides global).

class Filter:
    class Valves(BaseModel):
        API_KEY: str = Field(default="", description="Global API Key")
        
    class UserValves(BaseModel):
        API_KEY: str = Field(default="", description="User Private API Key")
        
    def inlet(self, body, __user__):
        # Prioritize user's Key
        user_valves = __user__.get("valves", self.UserValves())
        api_key = user_valves.API_KEY or self.valves.API_KEY

3. Deep Dive into Plugin Types

3.1 Action

Role: Adds buttons below messages that trigger upon user click.

Advanced Usage: Execute JavaScript on Frontend (File Download Example)

import base64

async def action(self, body, __event_call__):
    # 1. Generate content on backend
    content = "Hello OpenWebUI".encode()
    b64 = base64.b64encode(content).decode()
    
    # 2. Send JS to frontend for execution
    js = f"""
    const blob = new Blob([atob('{b64}')], {{type: 'text/plain'}});
    const a = document.createElement('a');
    a.href = URL.createObjectURL(blob);
    a.download = 'hello.txt';
    a.click();
    """
    await __event_call__({"type": "execute", "data": {"code": js}})

3.2 Filter

Role: Middleware that intercepts and modifies requests/responses.

inlet: Before request. Used for injecting context, modifying model parameters.
outlet: After response. Used for formatting output, logging.
stream: During streaming. Used for real-time sensitive word filtering.

Example: Injecting Environment Variables

async def inlet(self, body, __metadata__):
    vars = __metadata__.get("variables", {})
    context = f"Current Time: {vars.get('{{CURRENT_DATETIME}}')}"
    
    # Inject into System Prompt or first message
    if body.get("messages"):
        body["messages"][0]["content"] += f"\n\n{context}"
    return body

3.3 Pipe

Role: Custom Model/Agent.

Example: Simple OpenAI Wrapper

import requests

class Pipe:
    def pipes(self):
        return [{"id": "my-gpt", "name": "My GPT Wrapper"}]

    def pipe(self, body):
        # Modify body here, e.g., force add prompt
        headers = {"Authorization": f"Bearer {self.valves.API_KEY}"}
        r = requests.post("https://api.openai.com/v1/chat/completions", json=body, headers=headers, stream=True)
        return r.iter_lines()

4. Advanced Development Patterns

4.1 Pipe & Filter Collaboration

Use __request__.app.state to share data between plugins.

Pipe: __request__.app.state.search_results = [...]
Filter (Outlet): Read search_results and format them as citation links appended to the response.

4.2 Async Background Tasks

Execute time-consuming operations (e.g., summarization, database storage) in the background without blocking the user response.

import asyncio

async def outlet(self, body, __metadata__):
    asyncio.create_task(self.background_job(__metadata__["chat_id"]))
    return body

async def background_job(self, chat_id):
    # Execute time-consuming operation...
    pass

5. Best Practices & Design Principles

5.1 Naming & Positioning

Short & Punchy: e.g., "FlashCard", "DeepRead". Avoid generic terms like "Text Analysis Assistant".
Complementary: Don't reinvent the wheel; clarify what specific problem your plugin solves.

5.2 User Experience (UX)

Timely Feedback: Send a notification ("Generating...") before time-consuming operations.
Visual Appeal: When Action outputs HTML, use modern CSS (rounded corners, shadows, gradients).
Smart Guidance: If text is too short, prompt the user: "Suggest entering more content for better results".

5.3 Error Handling

Never let a plugin fail silently. Catch exceptions and inform the user via __event_emitter__.

try:
    # Business logic
except Exception as e:
    await __event_emitter__({
        "type": "notification",
        "data": {"type": "error", "content": f"Processing failed: {str(e)}"}
    })

6. Repository Standards (openwebui-extensions)

6.1 Single-file i18n Requirement

In this repository, each plugin must use a single source file with built-in i18n logic. Do not split source code by language.

Required pattern: plugins/{type}/{name}/{name}.py
Required docs: README.md + README_CN.md

6.2 Safe Context Access (Required)

Prefer helper methods like _get_user_context and _get_chat_context instead of direct, fragile field access from __user__ / body.

6.3 Event and Logging Conventions

Use status/notification events for user-visible progress.
Use frontend console debug logs (execute) for live debugging during development.
Use Python logging for backend logs; avoid print() in production plugin code.

6.4 Frontend Language Detection and Timeout Guard

When reading frontend language via __event_call__, always use:

JS try...catch fallback return
backend asyncio.wait_for(..., timeout=2.0)

This prevents deadlocks when frontend execution fails.

6.5 Copilot SDK Tool Definition

For custom Copilot SDK tools, define explicit parameter schema using a pydantic.BaseModel and pass it with params_type in define_tool(...).

6.6 Copilot SDK Streaming Output Format

Use native <think>...</think> for reasoning output.
Ensure </think> is closed before normal content or tool cards.
For tool result cards, use native <details type="tool_calls" ...> format.
Escape attribute quotes in arguments and result as ".

6.7 Source-derived Production Patterns (Recommended)

The following patterns are extracted from github_copilot_sdk.py and workspace_file_manager.py:

Tool parameter anti-drift: define tools with params_type=BaseModel, and execute with model_dump(exclude_unset=True) so missing params do not become explicit None.
Tool name normalization: enforce ^[a-zA-Z0-9_-]+$; if non-ASCII names collapse, use an md5 suffix fallback to keep registration stable.
Workspace sandboxing: resolve and verify every path stays inside the workspace root to prevent traversal.
3-step file delivery: local write -> publish_file_from_workspace -> return /api/v1/files/{id}/content, with skip_rag=true metadata.
Dual upload channel: prefer API upload (S3-compatible), fallback to DB + local copy.
Streaming stability: close <think> before emitting assistant.message_delta content.
Native tool cards: emit <details type="tool_calls"> on tool.execution_complete with strict HTML escaping (", newline escaping).
TODO persistence linkage: on successful update_todo, sync both TODO.md and database state.

6.8 Full Source-derived Knowledge Base (from `plugins/`)

The following is a broader extraction from actions/, filters/, pipes/, pipelines/, and tools/:

Action input hygiene: normalize multimodal message content, strip old plugin HTML blocks (OPENWEBUI_PLUGIN_OUTPUT), and enforce minimum text length before expensive model calls.
Action i18n hardening: use TRANSLATIONS + fallback_map + base-lang fallback (fr-CA -> fr-FR, en-GB -> en-US), keep all status/UI/JS strings in i18n keys, and protect format(**kwargs) formatting.
Frontend language detection (production-safe): use priority chain document.lang -> localStorage(locale/language) -> navigator.language -> profile/request, and always wrap __event_call__(execute) with timeout.
Long-running UX pattern: emit immediate status + notification, report staged progress (analyzing/rendering/saving), and keep detailed exception data in backend logs.
HTML plugin composability: use insertion markers for style/content/script, support both overwrite (CLEAR_PREVIOUS_HTML) and merge mode, and keep wrappers deterministic.
Theme-aware iframe rendering: detect theme from parent meta/class/data-theme with system fallback, and inject theme-aware colors for SVG/PNG export.
Client-side render-and-export pipeline: render offscreen chart/mindmap, export SVG/PNG, upload via /api/v1/files/, and persist updates through event API + chat persistence API.
DOCX export production patterns: apply TITLE_SOURCE fallback chain (chat_title -> markdown_title -> user+date), remove reasoning blocks, convert LaTeX via latex2mathml + mathml2omml, and emit citation-aware references/bookmarks.
OpenWebUI file retrieval fallback ladder: DB inline bytes/base64 -> S3 direct read -> local path variants -> public URL -> internal /api/v1/files/{id}/content -> raw object attrs, with max-byte guards at every stage.
Filter singleton-safe design: never store request-scoped mutable state on self; compute per-request values from body and context helpers.
Async context compression patterns: two-phase flow (inlet apply summary, outlet async generate summary), model-level threshold overrides, fast estimate + precise count near limit, and system-message protection (effective_keep_first).
Model compatibility guardrails: skip incompatible model families (e.g., copilot_sdk paths) and avoid hardcoded default model IDs.
Folder memory pattern: trigger periodic rule extraction (every N messages), replace rules idempotently using block markers (RULES_BLOCK_START/END), and optionally update root folder.
Tool workspace hardening: all file APIs (list/read/write/delete/publish) must re-check sandbox boundary, enforce size limits, and return user-ready download hints.
MoE prompt refiner pattern (pipeline): detect aggregation prompts via trigger prefix, parse original query + segmented responses, then rewrite to synthesis-oriented master prompt with optional aggregation model reroute.

6.9 Copilot-related Engineering Configuration

To support plugin engineering with GitHub Copilot + Gemini CLI + antigravity mode, adopt these controls:

Primary/secondary assistant lanes: Copilot is primary implementation lane; Gemini CLI is secondary draft/verification lane.
Single merge contract: both lanes must pass the same repository constraints (single-file i18n, context helpers, event conventions, release workflow rules).
Tool schema discipline: all Copilot SDK tools use explicit params_type with Pydantic models.
Antigravity safety: small reversible edits, timeout guards, fallback routing, and deterministic file/output paths.
File creation protocol: write in workspace scope, publish via workspace publish flow, return /api/v1/files/{id}/content for delivery.

Detailed design document:

docs/development/copilot-engineering-plan.md

7. Custom Agent Design Recommendations

7.1 Suggested architecture (for this repo)

Orchestrator Pipe: session lifecycle, model routing, streaming events.
Tool Adapter Layer: unify OpenWebUI Tools / OpenAPI / MCP with param validation and name normalization.
Workspace I/O Layer: sandboxed file operations + publish pipeline.
Render Layer: <think> lifecycle, tool cards, status/notification events.

7.2 MVP checklist

Dual config model: Valves + UserValves (user overrides first).
Unified context helpers: _get_user_context / _get_chat_context.
At least one artifact-delivery tool (e.g., publish_file_from_workspace).
Minimal streaming loop: reasoning_delta, message_delta, tool.execution_complete.
Unified error reporting via notification events.

7.3 Three high-impact agents you can build now

Repo Analyst Agent: output architecture map, risk list, and refactor proposals.
Release Draft Agent: generate Conventional Commit title/body + bilingual release summary.
Docs Sync Agent: compare source/doc versions and output a concrete sync file list.

7.4 Implementation priority

P0: Release Draft Agent (highest ROI, lowest risk).
P1: Docs Sync Agent (reduces doc drift).
P2: Repo Analyst Agent (medium/long-term evolution).

8. Troubleshooting

HTML not showing? Ensure it's wrapped in a ```html ... ``` code block.
Database error? Check if you called synchronous DB methods directly in an async function; use asyncio.to_thread.
Parameters not working? Check if Valves are defined correctly and if they are being overridden by UserValves.

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