Tnixc · Tnixc · Nov 5, 2025 · Nov 5, 2025 · Nov 5, 2025 · Nov 5, 2025
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -13,6 +13,7 @@ authors = ["Tnixc <tnixxc@gmail.com>"]
 color-print = "0.3.6"
 comrak = "0.26.0"
 fancy-regex = "0.13.0"
+katex = "0.4"
 minify-html = "0.15.0"
 notify = "6.1.1"
 num_cpus = "1.16.0"
@@ -22,6 +23,6 @@ serde_json = "1.0.120"
 simple-websockets = "0.1.6"
 
 [[bin]]
-name = "replacer"
+name = "simple"
 path = "src/main.rs"
 
diff --git a/README.md b/README.md
@@ -1,7 +1,7 @@
 # Simple Build tool
 
-> [!WARNING] 
-> Probably very buggy, it's very opiniated and not extensible.
+> [!WARNING]
+> Probably very buggy, it's very opinionated and not extensible.
 
 A simple build tool that assembles a static site from components, templates, and
 data. I used it to build v6 of https://enochlau.com
@@ -25,10 +25,6 @@ data. I used it to build v6 of https://enochlau.com
 
 - [ ] Improve JSON parsing error handling
 
-### Markdown and Content
-
-- [ ] LaTex?
-
 ### Errors/Logging
 
 - [ ] Exact file and line in error messages
@@ -44,6 +40,7 @@ data. I used it to build v6 of https://enochlau.com
 
 ### Done
 
+- [x] KaTeX support
 - [x] Handle port collisions in dev server
 - [x] Resolve dual sources of truth for Markdown frontmatter in blog posts (can't fix without proper Markdown parsing into entries)
 - [x] Bi-directional editing: You can now double click on a rendered `<markdown>` element to edit it, and it's reflected in the source code.
@@ -189,7 +186,7 @@ Will render out to:
 <img src="image.webp" alt="alt" />
 ```
 
-> [!NOTE] 
+> [!NOTE]
 > You can double click on a rendered markdown element and edit it from the web. The changes will be reflected in the source file. It is a bit flakely with escaped html entities, so try to avoid using those.
 
 ### Template entries

diff --git a/src/handlers/entries.rs b/src/handlers/entries.rs
@@ -1,5 +1,6 @@
 use crate::dev::{SCRIPT, WS_PORT};
 use crate::error::{ErrorType, ProcessError, WithItem};
+use crate::handlers::katex_assets;
 use crate::handlers::pages::page;
 use crate::utils::kv_replace;
 use crate::IS_DEV;
@@ -16,6 +17,9 @@ pub fn process_entry(
     let mut errors: Vec<ProcessError> = Vec::new();
     let is_dev = *IS_DEV.get().unwrap();
 
+    // Reset KaTeX usage flag for this page
+    katex_assets::reset_katex_flag();
+
     if entry_path.is_empty() || result_path.is_empty() {
         return vec![ProcessError {
             error_type: ErrorType::Other,
@@ -91,6 +95,20 @@ pub fn process_entry(
 
     let mut s = page_result.output;
 
+    // Inject KaTeX CSS if math was rendered (unless disabled)
+    if katex_assets::was_katex_used() && !katex_assets::is_katex_injection_disabled() {
+        // Print message once
+        katex_assets::print_katex_message();
+
+        // Inject CSS link in <head>
+        if s.contains("<head>") {
+            s = s.replace("<head>", &format!("<head>\n{}", katex_assets::get_katex_css_tag()));
+        } else {
+            // If no <head> tag, prepend to document
+            s = format!("{}\n{}", katex_assets::get_katex_css_tag(), s);
+        }
+    }
+
     if is_dev && !s.contains("// * SCRIPT INCLUDED IN DEV MODE") {
         s = s.replace("<head>", &format!("<head>{}", SCRIPT));
         s = s.replace(

diff --git a/src/handlers/katex_assets.rs b/src/handlers/katex_assets.rs
@@ -0,0 +1,38 @@
+use once_cell::sync::Lazy;
+use std::env;
+use std::sync::atomic::{AtomicBool, Ordering};
+
+// Track if KaTeX was used in the current page (thread-local)
+thread_local! {
+    static KATEX_USED: AtomicBool = const { AtomicBool::new(false) };
+}
+
+// Track if we've printed the KaTeX message (global, one-time)
+static MESSAGE_PRINTED: Lazy<AtomicBool> = Lazy::new(|| AtomicBool::new(false));
+
+pub fn mark_katex_used() {
+    KATEX_USED.with(|used| used.store(true, Ordering::Relaxed));
+}
+
+pub fn was_katex_used() -> bool {
+    KATEX_USED.with(|used| used.load(Ordering::Relaxed))
+}
+
+pub fn reset_katex_flag() {
+    KATEX_USED.with(|used| used.store(false, Ordering::Relaxed));
+}
+
+pub fn print_katex_message() {
+    if !MESSAGE_PRINTED.swap(true, Ordering::Relaxed) {
+        println!("  📐 KaTeX CSS will be injected (using CDN)");
+    }
+}
+
+pub fn is_katex_injection_disabled() -> bool {
+    env::var("SIMPLE_DISABLE_KATEX_CSS").is_ok()
+}
+
+pub fn get_katex_css_tag() -> &'static str {
+    r#"<!-- KaTeX CSS (auto-injected from CDN) -->
+<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/katex.min.css" integrity="sha384-nB0miv6/jRmo5UMMR1wu3Gz6NLsoTkbqJghGIsx//Rlm+ZU03BU6SQNC66uf4l5+" crossorigin="anonymous">"#
+}