diff --git a/src/catalog.js b/src/catalog.js
index 9495c30..1f61f1a 100644
--- a/src/catalog.js
+++ b/src/catalog.js
@@ -42,6 +42,15 @@ export const cacheRules = [
   },
 ];
 
+/**
+ * Find the catalog rule for a path relative to a scan root.
+ *
+ * Windows paths are normalized to lowercase to match the platform filesystem's
+ * case-insensitive behavior.
+ *
+ * @param {string} relativePath Path relative to the scan root.
+ * @returns {{ id: string, label: string, matches: Array<Function> } | undefined}
+ */
 export function findCacheRule(relativePath) {
   const parts = relativePath
     .split(/[\\/]+/)
@@ -53,6 +62,13 @@ export function findCacheRule(relativePath) {
   );
 }
 
+/**
+ * Resolve a candidate path into the relative form used by cache catalog checks.
+ *
+ * @param {string} root Scan root.
+ * @param {string} candidate Candidate cache path.
+ * @returns {string} Candidate path relative to the resolved root.
+ */
 export function relativeCachePath(root, candidate) {
   return path.relative(path.resolve(root), path.resolve(candidate));
 }
diff --git a/src/cleaner.js b/src/cleaner.js
index feec42a..dbe2070 100644
--- a/src/cleaner.js
+++ b/src/cleaner.js
@@ -20,6 +20,16 @@ function assertSafeTarget(root, candidate) {
   return rule;
 }
 
+/**
+ * Remove cache directories that still match the catalog under the scan root.
+ *
+ * Each target is resolved again before deletion so stale scan results cannot
+ * remove paths outside the root or paths that no longer look like known caches.
+ *
+ * @param {string} root Original scan root.
+ * @param {Array<object>} caches Cache entries returned by the scanner/filter.
+ * @returns {Promise<Array<object>>} Removal results with `removed` or `failed` status.
+ */
 export async function removeCaches(root, caches) {
   const resolvedRoot = path.resolve(root);
   const results = [];
diff --git a/src/cli.js b/src/cli.js
index 80858a1..640bcb8 100644
--- a/src/cli.js
+++ b/src/cli.js
@@ -16,6 +16,13 @@ async function readVersion() {
   return packageJson.version;
 }
 
+/**
+ * Execute the CLI command and return a process-style exit code.
+ *
+ * @param {string[]} args Raw command-line arguments without the executable name.
+ * @param {{ log: Function, error: Function }} [io] Output adapter for tests.
+ * @returns {Promise<number>} Exit code.
+ */
 export async function run(args, io = console) {
   let options;
   try {
diff --git a/src/filter.js b/src/filter.js
index 0af34b1..b0f805a 100644
--- a/src/filter.js
+++ b/src/filter.js
@@ -1,3 +1,11 @@
+/**
+ * Apply user-selected type, size, and age constraints to scanned cache entries.
+ *
+ * @param {Array<object>} caches Cache entries returned by the scanner.
+ * @param {{ minSize?: number, olderThan?: number, types?: Set<string> }} options
+ * @param {number} [now] Timestamp used for age comparisons.
+ * @returns {Array<object>} Cache entries that match all active filters.
+ */
 export function filterCaches(
   caches,
   { minSize = 0, olderThan = 0, types = new Set() },
diff --git a/src/options.js b/src/options.js
index 43f9bcb..91106a7 100644
--- a/src/options.js
+++ b/src/options.js
@@ -26,6 +26,13 @@ function readValue(args, index, flag) {
   return value;
 }
 
+/**
+ * Parse CLI arguments into normalized scan, filter, and output options.
+ *
+ * @param {string[]} args Raw command-line arguments without the executable name.
+ * @param {string} [cwd] Current working directory used to resolve the root.
+ * @returns {object} Normalized CLI options.
+ */
 export function parseOptions(args, cwd = process.cwd()) {
   const options = {
     root: cwd,
diff --git a/src/report.js b/src/report.js
index b579409..92e923e 100644
--- a/src/report.js
+++ b/src/report.js
@@ -4,6 +4,12 @@ function pad(value, width) {
   return String(value).padEnd(width);
 }
 
+/**
+ * Build aggregate counts for a cache result set.
+ *
+ * @param {Array<object>} caches Cache entries included in a report.
+ * @returns {{ directories: number, files: number, bytes: number }}
+ */
 export function createSummary(caches) {
   return {
     directories: caches.length,
@@ -12,6 +18,12 @@ export function createSummary(caches) {
   };
 }
 
+/**
+ * Render a human-readable scan report for terminal output.
+ *
+ * @param {object} report Scan, warning, and optional removal details.
+ * @returns {string} Formatted text report.
+ */
 export function formatTextReport({
   root,
   caches,
@@ -82,6 +94,12 @@ export function formatTextReport({
   return lines.join("\n");
 }
 
+/**
+ * Render a stable JSON report for scripts and CI jobs.
+ *
+ * @param {object} report Scan, warning, and optional removal details.
+ * @returns {string} Pretty-printed JSON report.
+ */
 export function formatJsonReport({
   root,
   caches,
diff --git a/src/scanner.js b/src/scanner.js
index cdadfc1..ced506e 100644
--- a/src/scanner.js
+++ b/src/scanner.js
@@ -51,6 +51,16 @@ async function measureDirectory(directory, warnings) {
   return measurement;
 }
 
+/**
+ * Walk a repository tree and return directories that match the cache catalog.
+ *
+ * The scanner skips symbolic links, avoids `.git`, records read failures as
+ * warnings, and measures each matched cache before returning it.
+ *
+ * @param {string} root Directory to scan.
+ * @param {{ maxDepth?: number }} [options] Traversal options.
+ * @returns {Promise<{ root: string, caches: Array<object>, warnings: string[] }>}
+ */
 export async function scanCaches(root, { maxDepth = 12 } = {}) {
   const resolvedRoot = path.resolve(root);
   const rootStats = await lstat(resolvedRoot);
diff --git a/src/units.js b/src/units.js
index fb957d8..0dc9947 100644
--- a/src/units.js
+++ b/src/units.js
@@ -29,14 +29,32 @@ function parseUnitValue(input, units, label) {
   return Number(match[1]) * multiplier;
 }
 
+/**
+ * Parse a size string such as `10mb` into bytes.
+ *
+ * @param {string} input Size value with a supported unit suffix.
+ * @returns {number} Rounded byte count.
+ */
 export function parseSize(input) {
   return Math.round(parseUnitValue(input, sizeUnits, "size"));
 }
 
+/**
+ * Parse a duration string such as `7d` into milliseconds.
+ *
+ * @param {string} input Duration value with a supported unit suffix.
+ * @returns {number} Rounded millisecond count.
+ */
 export function parseDuration(input) {
   return Math.round(parseUnitValue(input, durationUnits, "duration"));
 }
 
+/**
+ * Format a byte count for terminal reports.
+ *
+ * @param {number} bytes Byte count.
+ * @returns {string} Human-readable size.
+ */
 export function formatBytes(bytes) {
   if (bytes < 1024) {
     return `${bytes} B`;
@@ -56,6 +74,13 @@ export function formatBytes(bytes) {
   return `${value >= 10 ? value.toFixed(1) : value.toFixed(2)} ${unit}`;
 }
 
+/**
+ * Format elapsed time since a cache entry was last modified.
+ *
+ * @param {number} modifiedAtMs Last modified timestamp in milliseconds.
+ * @param {number} [now] Current timestamp for deterministic tests.
+ * @returns {string} Compact age string.
+ */
 export function formatAge(modifiedAtMs, now = Date.now()) {
   const elapsed = Math.max(0, now - modifiedAtMs);
   const hours = Math.floor(elapsed / (60 * 60_000));