LeetCoach

An AI coaching sidebar for LeetCode, powered by Claude. Get hints, code feedback, and algorithm guidance without leaving the problem page — no copy-pasting, no context switching.

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What it does

LeetCoach adds a sidebar directly to LeetCode problem pages. Instead of Googling hints or pasting your code into ChatGPT, you get a coaching assistant that already knows the problem you're on, the code you've written, and (when you've submitted) what went wrong.

Hint — progressive hints that reveal only as much as you need. Level 1 nudges you in the right direction. Level 2 names the category. Level 3 names the exact data structure. No spoilers unless you ask. In Interview mode, instead of a hint, the AI will ask you a clarifying question about your approach.

Analyze Code — reviews your current code in three dimensions: correctness (and why a failed submission failed), time/space complexity, and edge cases. In Interview mode, it will challenge your choices and ask you to justify your trade-offs.

DSA Tips — identifies the algorithmic pattern and optimal data structure for the problem in 1-3 lines. Useful when you're not sure where to start. In Interview mode, it will also ask you to explain why this choice is optimal.

Chat — freeform coaching. Ask follow-up questions, talk through your approach, or ask why your logic is wrong. In Interview mode, the AI acts as a senior technical interviewer, challenging your logic and logic and using Socratic questioning.

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Modes

LeetCoach has three coaching modes, toggled via the icon in the header:

• 🎓 Learn (Default) — Educational and encouraging. Explains concepts, names algorithms, and teaches syntax.
• 📝 Practice — Minimal nudges. No names, no syntax, no explanations. Just directional hints.
• 👔 Interview — Mock interview. The AI acts as a professional interviewer, asking clarifying questions, challenging trade-offs, and focusing on your communication skills.

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Install

Chrome Web Store — search "LeetCoach"

Developer mode:

1. Clone this repo
2. Go to chrome://extensions → enable Developer Mode
3. Click Load Unpacked → select the extension/ folder
4. Open any LeetCode problem — the sidebar opens automatically

Keyboard shortcut: Ctrl+Shift+L / Cmd+Shift+L to reopen the sidebar

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Usage limits

LeetCoach is free. Each LeetCode account gets 100 requests per week, resetting every Monday. The usage indicator in the top-right corner of the sidebar shows how many prompts you have left.

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Architecture

Chrome Extension (Manifest V3)
        │
        │  HTTPS (streamed)
        ▼
AWS Lambda (Python 3.11)
  ├── Amazon Bedrock  ──►  Claude Haiku 4.5   (hint, DSA)
  │                   ──►  Claude Sonnet 4.6  (analyze, chat)
  └── DynamoDB  ──►  leetcoach-users  (weekly usage tracking)

Extension

File	Role
manifest.json	Permissions, content scripts, side panel config, keyboard shortcut
background.js	Side panel enable/disable logic, keyboard shortcut handler
content.js	Reads LeetCode DOM — problem title, difficulty, tags, description, language, username
sidepanel.html	Sidebar UI markup and CSS
sidepanel.js	Chat logic, Monaco code reading (MAIN world), submission result scraping, Lambda fetch, usage tracking

User code is read via chrome.scripting.executeScript in the MAIN world — the extension's isolated content script cannot access the editor internals directly. The implementation tries Monaco first (first non-empty model), then CodeMirror 6 (via the internal EditorView key on .cm-editor), then falls back to reading .cm-line DOM elements. LeetCode migrated from Monaco to CM6, so most users hit the CM6 path.

Backend

Single Lambda function (backend/lambda_function.py) with a Function URL. The request mode field routes to the appropriate prompt and model:

Mode	Model	Max tokens
hint	Claude Haiku 4.5	64
dsa	Claude Haiku 4.5	128
analyze	Claude Sonnet 4.6	256
chat	Claude Sonnet 4.6	256

Responses are streamed via chunked transfer encoding posted directly to the Lambda Runtime API (/2018-06-01/runtime/invocation/{id}/response). Bootstrap's duplicate buffered post is suppressed by monkey-patching runtime_client.post_invocation_result (the C extension module).

DynamoDB

Tables:

• leetcoach-users — partition key userId (LeetCode username). Tracks weekly usage.
• leetcoach-problems — partition key problemSlug. Stores problem descriptions, solutions, hints, and topics.

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LeetCode Database

To provide richer coaching (hints, solutions, topics), LeetCoach uses a local DynamoDB table seeded with problem metadata.

Seeding the database:

1. The project includes a pre-configured script: scripts/upload_problems.py.
2. I have already downloaded the merged_problems.json dataset from the neenza/leetcode-problems repository.
3. To upload the data to your AWS account, ensure your AWS CLI is configured and run:

   python scripts/upload_problems.py

   Note: This script handles the DynamoDB 400KB item limit by truncating extremely large solutions or descriptions if necessary.

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Tech stack

• API key is a SAM parameter — never hardcoded in template.yaml; samconfig.toml is gitignored
• Billing kill switch: AWS Budgets Action attaches a Deny IAM policy at $10/month, cutting off all Bedrock calls

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Deploying the backend

Requires AWS CLI, SAM CLI, and Bedrock model access for claude-haiku-4-5 and claude-sonnet-4-6 in us-east-1.

sam build --use-container
sam deploy

On first deploy, SAM will prompt for the ApiKey parameter. Mirror the same value in extension/sidepanel.js.

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Tech stack

• Frontend: Chrome Extension (Manifest V3, vanilla JS)
• Backend: AWS Lambda (Python 3.11), AWS SAM
• AI: Amazon Bedrock — Claude Haiku 4.5, Claude Sonnet 4.6
• Database: Amazon DynamoDB (on-demand)
• Infra: AWS IAM, AWS Budgets, Amazon CloudWatch