AI That Lives Inside Your Browser
AI-powered browser extension development from the Philippines. I build Chrome extensions with built-in LLM features — OpenAI/Claude API integration, page summarization, writing assistants, and context-aware tools using Manifest V3.
AI tools ask users to leave the page. AI extensions bring the AI to the page.
ChatGPT and Claude are powerful — but they require users to copy content from one tab, paste it into another, wait for a response, and then copy the result back. That context switch breaks flow and happens dozens of times a day for knowledge workers who rely on AI to get things done.
AI browser extensions solve this by putting the AI directly on the page — reading the current content, responding in a sidebar, and writing back into the document. But building these extensions correctly requires handling API keys securely inside a sandboxed extension environment, managing streaming responses across content script boundaries, and keeping the extension fast enough to feel native.
AI browser extensions that feel native, not bolted on.
I build AI-powered Chrome extensions that integrate GPT-4o or Claude API directly into the browsing experience. Secure API key handling, streaming responses, context-aware prompting from page content, and sidebar UIs that feel like part of the browser. Based in Davao City, Philippines, I deliver remotely with async communication across US, AU, and EU timezones.
- API keys secured in background service worker — never exposed to page context
- Streaming responses rendered token-by-token for instant perceived performance
- Page content extraction from any site including SPAs and dynamic content
- Context-aware prompting using current page, selected text, or user clipboard
- Chrome Web Store submission with AI feature disclosure handled correctly
What I Build For You
Page Summarizer
Extracts and summarizes the content of any web page — articles, documentation, long-form reports — in a sidebar panel. Configurable summary length, bullet or prose format, and copy-to-clipboard output.
Writing Assistant
In-browser writing tool that activates on any editable field — Google Docs, email, CMS editors, and text inputs. Rewrites, expands, shortens, changes tone, and suggests continuations based on existing content.
AI Research Tool
Highlights key facts, surfaces related questions, and generates research summaries from the current page. Saves annotated snippets with AI commentary to a local research board exportable as markdown.
Email Assistant
Gmail and Outlook extension that reads the current email thread and suggests context-aware replies, reformats drafts, generates follow-up summaries, and identifies action items from long email chains.
AI Sidebar
A persistent AI assistant sidebar that stays open across page navigation. Context updates automatically to reflect the current page. Supports multi-turn conversations with page content as grounding context.
Data Extractor
AI-powered structured data extraction from any page — identifies and normalizes product details, contact information, table data, and pricing across inconsistently formatted pages, exported to CSV or webhook.
Transparent Pricing, No Retainer Required
One-time project fee
A single AI feature in a Chrome extension — summarizer, writing tool, or data extractor.
- Single AI feature (summarizer, writer, or extractor)
- GPT-4o or Claude API integration
- Secure API key storage in service worker
- Basic popup or sidebar UI
- Chrome Web Store submission assets
- 2 weeks post-launch support
One-time project fee
A full AI extension — sidebar, streaming responses, multi-feature, and user settings.
- Multi-feature AI extension with persistent sidebar
- Streaming response rendering (token-by-token display)
- Multi-turn conversation with page context grounding
- User settings for model, tone, and behavior preferences
- Conversation history with local storage persistence
- Chrome Web Store submission with AI feature disclosure
- 30 days post-launch support with check-ins
Scoped per project
Team-deployed AI extensions with shared context, usage controls, and backend logging.
- Enterprise Chrome policy deployment
- Shared organization context and knowledge base
- Usage controls and API cost budgeting per user
- Conversation logging to backend for compliance
- Admin dashboard for team AI configuration
- Custom model fine-tuning integration
- Retainer option for ongoing development
From AI Concept to Browser Extension
AI Feature Scoping
We define what the AI does, which sites it runs on, which model fits the task, and how the user interacts with AI responses. Model choice — GPT-4o vs. Claude — is decided by the specific task requirements.
Security and Architecture Design
API key handling architecture designed before development: service worker isolation, content script message passing boundaries, and streaming response pipeline from API to rendered UI.
AI Integration and UI Development
Extension built in TypeScript with React sidebar UI. AI streaming implemented via Server-Sent Events relayed through the background service worker. Content extraction logic built for target page types.
Prompt Engineering and Testing
System prompts refined against real page content — not synthetic test cases. Edge cases tested: very long pages, pages with no readable content, pages in multiple languages, and ambiguous user inputs.
Store Submission and Handoff
Chrome Web Store submission with AI feature disclosure handled according to current store policies. Source code, prompt templates, and deployment documentation delivered at handoff.
What Makes These AI Extensions Feel Native and Trustworthy
API Keys Never in Page Context
All AI API calls are made from the background service worker — a privileged context isolated from page JavaScript. User API keys stored via chrome.storage.local are never accessible to content scripts or the pages being browsed.
Streaming Responses Feel Instant
AI responses are streamed token-by-token from the API through the background service worker to the sidebar UI via Chrome message passing. The response starts appearing in under a second — no blank loading states.
Context Extracted From Any Page
Content extraction handles articles, documentation, SPAs, JavaScript-rendered content, and iframes. The AI always has the full relevant page context — not just visible viewport text.
Model Choice Based on Task
GPT-4o for complex reasoning and long-context tasks. Claude for nuanced writing assistance and structured extraction. GPT-4o-mini or Claude Haiku for high-frequency, cost-sensitive features. Model selection is a design decision — not a default.
Async-First Delivery
Based in Davao City, Philippines (UTC+8). Projects run async-first with Loom demos of working AI features and written progress updates. US, AU, and EU clients get full visibility without live scheduling pressure.
Chrome Web Store AI Disclosure
The Chrome Web Store requires specific disclosures for extensions that use AI or process user data with third-party APIs. Every submission I handle includes correct AI feature disclosure language that satisfies current store review requirements.
AI Extensions Built, Workflows Transformed
"Johnbert built an AI writing assistant extension for our editorial team. It activates in our CMS editor and rewrites drafts to match our brand voice guidelines — which he loaded into the system prompt as structured context. The quality is high enough that editors treat it as a first-pass collaborator, not a gimmick."
"The AI research sidebar JB built has genuinely changed how our team reads long reports. It surfaces key claims, flags contradictions with prior context, and lets analysts ask follow-up questions without leaving the document. The streaming response implementation makes it feel faster than ChatGPT even though it uses the same API."
"We needed an extension that reads prospect LinkedIn profiles and generates personalized email openers using Claude. Johnbert built it in three weeks — the structured data extraction from LinkedIn profiles is accurate, the prompts produce emails that sound human, and our BDRs have cut email drafting time by about 70%."
AI Browser Extension Questions, Answered
Johnbert Oñez
AI Solutions Engineer & Full Stack Developer · 6+ yrs · 50+ projects
Based in Davao City, Philippines. Specialises in production AI systems, full-stack web applications, and WordPress. Remote-first, async-friendly, fixed-fee projects.
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