KestrelCP

A VS Code extension for competitive programming — scaffold problems from URLs, run tests against bundled cases, and commit with AI-generated messages, all without leaving the editor.

[!NOTE] This extension is primarily built for my personal use — a local environment to debug and implement competitive programming solutions from Kattis, Codeforces, and LeetCode. Kattis and Codeforces solutions still need to be manually submitted on each platform's official site; LeetCode can be submitted directly from the editor. A nice side benefit: committing solutions to a Git repo helps keep your GitHub contribution graph active.

Currently only Java is supported as the solution language. Support for other languages may come in the future.

If you find it useful, feel free to use it! Suggestions and new features are welcome via pull requests.

Check out cp-solutions-vault to see the extension in action with a real workspace.

⚡ What it does

• Scaffold a problem folder from a Kattis / Codeforces / LeetCode URL. Sample test cases are auto-fetched.
• Search LeetCode by title or keyword and pick a problem to scaffold.
• Test your Solution.java with one click on the editor toolbar (top-right of the editor). LeetCode problems are run on LeetCode's official judge.
• Submit to LeetCode with one click on the editor toolbar — counts as an official submission, shows runtime / memory percentile.
• Commit with a Conventional-Commits message generated by Claude from your staged diff.
• LeetCode Daily Challenge widget in the sidebar — today's problem is one click away. Click to scaffold (or open if already done).
• Playground — a dedicated playground/Playground.java for ad-hoc Java experimentation. One click on the editor toolbar compiles and runs it.

🚀 Install

Search for KestrelCP in the VS Code Extensions panel and click Install.

Or from the command line:

code --install-extension khoa-doan.kestrelcp

Alternatively, .vsix builds are attached to GitHub Releases for manual installation.

Requirements

• Python 3 with requests, beautifulsoup4, anthropic

  pip3 install requests beautifulsoup4 anthropic
  

• JDK 17+ (javac and java on PATH)
• Anthropic API key for KestrelCP: AI Commit — store it via the command palette → KestrelCP: Set Anthropic API Key (saves to VS Code's encrypted SecretStorage, not plain settings.json). Or export ANTHROPIC_API_KEY=sk-ant-… in your shell as a fallback.
• LeetCode cookies (only if you want to run / submit LeetCode problems — scaffolding and search work without them). See LeetCode setup below.

🎯 Daily workflow

1. Open VS Code on a folder — either an existing CP folder or a brand-new one.

2. First time only (required): run KestrelCP: Initialize Workspace from the command palette to create the kattis/, codeforces/, leetcode/, and playground/Playground.java scaffolding. All other commands require the workspace to be initialized first.

3. Scaffold a new problem — three entry points, all via the command palette (Cmd+Shift+P):

   • KestrelCP: New Problem — pick platform, paste the problem URL
   • KestrelCP: Search LeetCode — type a title or keyword, pick from the results
   • Click the LeetCode Daily Challenge entry in the KestrelCP sidebar to scaffold today's problem in one click

   Solution.java opens automatically once scaffolding finishes. For LeetCode, it's the exact starter code shown in LeetCode's web editor (correct method signature, helper class imports, etc.) — you fill in the method body.

4. Solve it.

5. Run tests — click the ▶ button in the editor toolbar (top-right of the editor, visible whenever you're on a Solution.java), or Cmd+Shift+P → KestrelCP: Run Tests for Current Problem.

   For Kattis / Codeforces, this runs javac + java locally against your *.in / *.out files. For LeetCode, this batches all *.in files into one call to LeetCode's "Run Code" judge (the same one their web editor uses) and reports per-case PASS / FAIL.

6. Submit (LeetCode only) — click the ☁️ button in the editor toolbar (only shown on a LeetCode Solution.java), or Cmd+Shift+P → KestrelCP: Submit to LeetCode. Counts as an official submission and reports runtime / memory percentile.

7. Commit — stage your files in the Source Control panel, then Cmd+Shift+P → KestrelCP: AI Commit. Claude proposes a Conventional Commit message; type y / n / e to accept / abort / edit.

🧪 Playground

Need to try a snippet without scaffolding a whole problem? KestrelCP: Initialize Workspace also creates playground/Playground.java — a free-form Java scratchpad. Open it (e.g. Cmd+P → Playground.java) and hit the ▶ button in the editor toolbar to compile + run. Add helper classes alongside it (Helper.java, etc.) — javac *.java picks them up automatically; java Playground is the entry point.

🎯 LeetCode Daily Challenge

The KestrelCP sidebar (cube icon in the activity bar) shows today's LeetCode Daily Challenge with its difficulty and acceptance rate. Click the row to scaffold it in one step; if you've already started it today, the click opens your existing Solution.java. The 🔄 button on the view title forces a re-fetch. No auth required for this — the daily-challenge endpoint is public.

🔑 LeetCode setup

Scaffolding LeetCode problems and searching the catalog work anonymously, but running tests and submitting require LeetCode's own session cookies — there is no public LeetCode API, so KestrelCP authenticates the same way your browser does.

One-time setup:

1. Log in to leetcode.com in your browser.
2. DevTools → Application → Cookies → https://leetcode.com (Chrome / Edge), or Storage → Cookies (Firefox).
3. Copy the values of these two cookies:
   • LEETCODE_SESSION (long JWT, ~600 chars)
   • csrftoken (~32 chars)
4. Command palette → KestrelCP: Set LeetCode Cookies. Paste each value when prompted.

Cookies are stored in VS Code's SecretStorage (encrypted via the OS keychain), not in settings.json.

Expiry: LEETCODE_SESSION is a JWT that lasts about 2 weeks; csrftoken is effectively long-lived. KestrelCP decodes the JWT and refuses to make a doomed call when it's already expired — it tells you precisely which cookie to refresh:

• 🔑 "LEETCODE_SESSION expired on YYYY-MM-DD" → re-paste fresh cookies.
• 🛡️ "LeetCode rejected the csrftoken" → re-paste both (they're usually rotated together).
• ⏳ "LeetCode is rate-limiting" → wait a few seconds and try again.

To clear: run KestrelCP: Set LeetCode Cookies again and submit empty values for one or both prompts — empty input clears that secret.

📋 Commands

⚙️ Settings

Sensitive values (Anthropic API key, LeetCode cookies) are not stored in settings — they live in VS Code's encrypted SecretStorage. Use the KestrelCP: Set ... commands to manage them.

KestrelCP invokes python3 directly — it expects Python 3 to be on PATH and will show an error on activation if python3 --version fails. Users with a virtualenv should activate it before launching VS Code.

🔍 How it works

• Scaffolding (Kattis / Codeforces) parses HTML with requests + BeautifulSoup and writes one *.in / *.out pair per sample.
• Scaffolding (LeetCode) uses LeetCode's public GraphQL endpoint to pull exampleTestcases, codeSnippets (the editor's Java template), and the HTML problem statement. No auth needed for non-premium problems.
• Testing (Kattis / Codeforces) runs javac Solution.java, then java Solution once per *.in with stdin redirected. Output is compared to the matching *.out ignoring trailing whitespace and blank lines. 5-second timeout per case.
• Testing (LeetCode) reads every *.in for the problem, concatenates them into a single data_input, and POSTs to LeetCode's interpret_solution endpoint (the "Run Code" button). The judge runs every case in one container and returns parallel code_answer / expected_code_answer arrays. End-to-end latency is typically ~1-2 seconds regardless of case count, since the cost is dominated by judge container spin-up.
  • For sample cases, KestrelCP honors LeetCode's overall verdict (status_msg: "Accepted") even when string equality disagrees — so multi-valid-answer problems (e.g. two-sum returning [1,0] instead of [0,1]) don't get false FAILs.
  • For custom inputs (any <N>.in you add that LeetCode hasn't seen), there's no reference to compare against; the output is shown without a verdict so you can eyeball it. Local <N>.out files are deliberately not used for comparison.
• Submitting (LeetCode) POSTs to /problems/<slug>/submit/ and polls until the judge returns the verdict (Accepted / Wrong Answer / TLE / Compile Error / Runtime Error). On Accepted, reports the runtime and memory percentile.
• AI Commit runs git diff --staged, asks Claude for a one-line Conventional Commit message with an emoji prefix:

Confirm with y (accept), n (abort), or e (edit before committing).

🛠️ Contributing / development

Working on the extension itself? Head to the GitHub repo for the dev loop, manual test plan, scraper canary, and release process.

🪪 License

MIT — see LICENSE.