diff --git a/src/lib.rs b/src/lib.rs
index fb910bc953..6faf7ad1ba 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,14 @@
+use std::path::Path;
+
+use anyhow::Result;
+use log::debug;
+use rustpython_parser::lexer::LexResult;
+
+use crate::autofix::fixer::Mode;
+use crate::linter::{check_path, tokenize};
+use crate::message::Message;
+use crate::settings::Settings;
+
 mod ast;
 mod autofix;
 pub mod cache;
@@ -13,3 +24,49 @@ pub mod printer;
 pub mod pyproject;
 mod python;
 pub mod settings;
+
+/// Run ruff over Python source code directly.
+pub fn check(path: &Path, contents: &str) -> Result<Vec<Message>> {
+    // Find the project root and pyproject.toml.
+    let project_root = pyproject::find_project_root(&[path.to_path_buf()]);
+    match &project_root {
+        Some(path) => debug!("Found project root at: {:?}", path),
+        None => debug!("Unable to identify project root; assuming current directory..."),
+    };
+    let pyproject = pyproject::find_pyproject_toml(&project_root);
+    match &pyproject {
+        Some(path) => debug!("Found pyproject.toml at: {:?}", path),
+        None => debug!("Unable to find pyproject.toml; using default settings..."),
+    };
+
+    let settings = Settings::from_pyproject(pyproject, project_root)?;
+
+    // Tokenize once.
+    let tokens: Vec<LexResult> = tokenize(contents);
+
+    // Determine the noqa line for every line in the source.
+    let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
+
+    // Generate checks.
+    let checks = check_path(
+        path,
+        contents,
+        tokens,
+        &noqa_line_for,
+        &settings,
+        &Mode::None,
+    )?;
+
+    // Convert to messages.
+    let messages: Vec<Message> = checks
+        .into_iter()
+        .map(|check| Message {
+            kind: check.kind,
+            fixed: check.fix.map(|fix| fix.applied).unwrap_or_default(),
+            location: check.location,
+            filename: path.to_string_lossy().to_string(),
+        })
+        .collect();
+
+    Ok(messages)
+}
diff --git a/src/linter.rs b/src/linter.rs
index 179b176893..098d1755ed 100644
--- a/src/linter.rs
+++ b/src/linter.rs
@@ -16,7 +16,7 @@ use crate::settings::Settings;
 use crate::{cache, fs, noqa};
 
 /// Collect tokens up to and including the first error.
-fn tokenize(contents: &str) -> Vec<LexResult> {
+pub(crate) fn tokenize(contents: &str) -> Vec<LexResult> {
     let mut tokens: Vec<LexResult> = vec![];
     for tok in lexer::make_tokenizer(contents) {
         let is_err = tok.is_err();
@@ -28,7 +28,7 @@ fn tokenize(contents: &str) -> Vec<LexResult> {
     tokens
 }
 
-fn check_path(
+pub(crate) fn check_path(
     path: &Path,
     contents: &str,
     tokens: Vec<LexResult>,
diff --git a/src/main.rs b/src/main.rs
index 80c3120aab..e3617c3a46 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -23,9 +23,9 @@ use ::ruff::logging::set_up_logging;
 use ::ruff::message::Message;
 use ::ruff::printer::{Printer, SerializationFormat};
 use ::ruff::pyproject::{self, StrCheckCodePair};
+use ::ruff::settings::CurrentSettings;
 use ::ruff::settings::{FilePattern, PerFileIgnore, Settings};
 use ::ruff::tell_user;
-use ruff::settings::CurrentSettings;
 
 const CARGO_PKG_NAME: &str = env!("CARGO_PKG_NAME");
 const CARGO_PKG_VERSION: &str = env!("CARGO_PKG_VERSION");