LSP Diagnostics — Code Checked While You Type

Think of a spell-checker for your writing, but for code — that’s LSP Diagnostics.

What Is an LSP, Anyway?

LSP stands for Language Server Protocol. It’s a behind-the-scenes helper that your code editor talks to. When you type, the editor sends your code to the language server, which checks for mistakes and sends back suggestions. You see the result as red squiggly underlines, yellow warnings, or little lightbulb icons.

In Hermes Agent, we use LSP to give you instant feedback while you write — no need to run a separate “check” command. It’s like having a patient senior developer peeking over your shoulder, pointing out typos and logic slips before you even save the file.

Why Should Beginners Care?

You don’t need to know how LSP works internally. But you do need to know that:

It catches simple mistakes (missing brackets, wrong variable names) immediately.
It teaches you as you go — hover over a squiggle to see the problem and a fix.
It saves time — you fix issues while they’re fresh, not after a long debugging session.

How to Use LSP Diagnostics in Hermes Agent

Hermes Agent comes with LSP support built in. Here’s how to get started:

1. Open Your Project

Make sure you’re in the folder with your code. In your terminal:

cd my-project

2. Start Hermes Agent’s Editor Integration

Run this command (or use the shortcut in your editor):

hermes lsp start

Now, open any .py, .js, .ts, or .go file. You’ll see diagnostics appear automatically.

3. Read the Diagnostic Panel

In most editors, press:

Ctrl+Shift+M   (Windows/Linux)
Cmd+Shift+M    (Mac)

This opens the “Problems” panel. It lists every issue, with the file name, line number, and a short description.

4. Apply Quick Fixes

Click on a squiggly line. A small popup will appear. Choose “Quick Fix” or press:

Ctrl+.   (Windows/Linux)
Cmd+.    (Mac)

Hermes Agent will suggest a fix — often just one keystroke to accept it.

What Do the Symbols Mean?

Red underline = error. Something is definitely wrong (e.g., undefined function).
Yellow underline = warning. Not fatal, but likely a bug (e.g., unused variable).
Blue/lightbulb = suggestion. Optional improvement (e.g., simplify this code).

A Real Example

Let’s say you type this in Python:

def greet(name):
    print("Hello, " + nam)

Notice the nam — a typo. The LSP will underline it in red. Hover over it, and you’ll see:

Name "nam" is not defined. Did you mean "name"?

Click the quick fix, and it changes to name automatically. You just avoided a crash.

Common Pitfalls (And How to Avoid Them)

Don’t ignore warnings — they often point to future bugs.
Check the panel regularly — not just the current line.
If you see “No LSP server found” — make sure you ran hermes lsp start and that your file type is supported.

Summary and Practical Tip

LSP Diagnostics give you real-time feedback, making coding feel more like a conversation than a guessing game. You write, the tool nudges, you fix — it’s that simple.

Practical tip: Before you run your code, always glance at the Problems panel. One quick look can save you ten minutes of “Why is this broken?” debugging. Make it a habit — your future self will thank you.

Now go write some code, and let the squiggles guide you.