Auto-Apply Extension — AI-Powered Job Application Chrome Extension

What it is

A Chrome extension that reads job postings and auto-fills application forms using the candidate's resume. Think "1-click apply" but actually intelligent — it understands form context and tailors responses, not just copy-pastes.

How it Works

1. Content Script — scrapes the job posting text and detects form fields on the current page.

2. Background Service Worker — sends the job description + user's stored profile to Claude.

3. AI Layer — Claude maps each form field (label + placeholder) to the right resume section and generates a tailored answer. Cover letter fields get a custom paragraph; skills fields get filtered to what's relevant.

4. Injection — content script fills fields programmatically, user reviews and submits.

Key Technical Challenges

• Form field detection: Job boards use wildly different HTML structures. Built a heuristic classifier (label text + input type + aria attributes) that hits ~90% accuracy across Greenhouse, Lever, Workday, LinkedIn.
• Context window management: Some job postings are 3000+ tokens. Used Claude Haiku for the fast "extract key requirements" step, then fed a compressed summary to Sonnet for the fill step.
• Latency: Users expect instant fill. Parallelized per-field API calls, targeting < 3s total for a 10-field form.

What I Learned

• Chrome's Manifest V3 service workers have strict memory limits — had to be careful about caching the user's profile in chrome.storage.local vs in-memory.
• Structured outputs (tool use) are essential here: free-form text responses are unpredictable when you need exact field values.

Tech Stack

TypeScript, Chrome Extension Manifest V3, Anthropic Claude (Haiku + Sonnet), Webpack, React (popup UI)