diff --git a/packages/router-core/src/defer.ts b/packages/router-core/src/defer.ts
index 1b3eb5b0f86..2bae16301f0 100644
--- a/packages/router-core/src/defer.ts
+++ b/packages/router-core/src/defer.ts
@@ -1,5 +1,10 @@
 import { defaultSerializeError } from './router'
 
+/**
+ * Well-known symbol used by {@link defer} to tag a promise with
+ * its deferred state. Consumers can read `promise[TSR_DEFERRED_PROMISE]`
+ * to access `status`, `data`, or `error`.
+ */
 export const TSR_DEFERRED_PROMISE = Symbol.for('TSR_DEFERRED_PROMISE')
 
 export type DeferredPromiseState<T> =
diff --git a/packages/router-core/src/path.ts b/packages/router-core/src/path.ts
index edb5a8d22cb..a0dcda2a060 100644
--- a/packages/router-core/src/path.ts
+++ b/packages/router-core/src/path.ts
@@ -66,6 +66,10 @@ export function removeTrailingSlash(value: string, basepath: string): string {
 // see the usage in the isActive under useLinkProps
 // /sample/path1 = /sample/path1/
 // /sample/path1/some <> /sample/path1
+/**
+ * Compare two pathnames for exact equality after normalizing trailing slashes
+ * relative to the provided `basepath`.
+ */
 export function exactPathTest(
   pathName1: string,
   pathName2: string,
@@ -222,6 +226,10 @@ export const parseRoutePathSegments = (
   cache?: ParsePathnameCache,
 ): ReadonlyArray<Segment> => parsePathname(pathname, cache, false)
 
+/**
+ * Parse a pathname into an array of typed segments used by the router's
+ * matcher. Results are optionally cached via an LRU cache.
+ */
 export const parsePathname = (
   pathname?: string,
   cache?: ParsePathnameCache,
diff --git a/packages/router-core/src/process-route-tree.ts b/packages/router-core/src/process-route-tree.ts
index 221cedc26de..85ba1475fda 100644
--- a/packages/router-core/src/process-route-tree.ts
+++ b/packages/router-core/src/process-route-tree.ts
@@ -184,6 +184,14 @@ export type ProcessRouteTreeResult<TRouteLike extends RouteLike> = {
   flatRoutes: Array<TRouteLike>
 }
 
+/**
+ * Build lookup maps and a specificity-sorted flat list from a route tree.
+ * Returns `routesById`, `routesByPath`, and `flatRoutes`.
+ */
+/**
+ * Build lookup maps and a specificity-sorted flat list from a route tree.
+ * Returns `routesById`, `routesByPath`, and `flatRoutes`.
+ */
 export function processRouteTree<TRouteLike extends RouteLike>({
   routeTree,
   initRoute,
diff --git a/packages/router-core/src/redirect.ts b/packages/router-core/src/redirect.ts
index 4672bf3febf..61e1e07ff16 100644
--- a/packages/router-core/src/redirect.ts
+++ b/packages/router-core/src/redirect.ts
@@ -71,6 +71,10 @@ export type ResolvedRedirect<
  * @returns A Response augmented with router navigation options.
  * @link https://tanstack.com/router/latest/docs/framework/react/api/router/redirectFunction
  */
+/**
+ * Create a redirect Response understood by TanStack Router.
+ * Use inside loaders/beforeLoad or server handlers to trigger navigation.
+ */
 export function redirect<
   TRouter extends AnyRouter = RegisteredRouter,
   const TTo extends string | undefined = '.',
@@ -109,11 +113,13 @@ export function redirect<
   return response as Redirect<TRouter, TFrom, TTo, TMaskFrom, TMaskTo>
 }
 
+/** Check whether a value is a TanStack Router redirect Response. */
 /** Check whether a value is a TanStack Router redirect Response. */
 export function isRedirect(obj: any): obj is AnyRedirect {
   return obj instanceof Response && !!(obj as any).options
 }
 
+/** True if value is a redirect with a resolved `href` location. */
 /** True if value is a redirect with a resolved `href` location. */
 export function isResolvedRedirect(
   obj: any,
@@ -121,6 +127,7 @@ export function isResolvedRedirect(
   return isRedirect(obj) && !!obj.options.href
 }
 
+/** Parse a serialized redirect object back into a redirect Response. */
 /** Parse a serialized redirect object back into a redirect Response. */
 export function parseRedirect(obj: any) {
   if (obj !== null && typeof obj === 'object' && obj.isSerializedRedirect) {
diff --git a/packages/router-core/src/root.ts b/packages/router-core/src/root.ts
index 6aa46e3eb99..361ffa9ea1b 100644
--- a/packages/router-core/src/root.ts
+++ b/packages/router-core/src/root.ts
@@ -1,2 +1,3 @@
+/** Stable identifier used for the root route in a route tree. */
 export const rootRouteId = '__root__'
 export type RootRouteId = typeof rootRouteId
diff --git a/packages/router-core/src/router.ts b/packages/router-core/src/router.ts
index 9ff9eb3dca6..fd97f6b132e 100644
--- a/packages/router-core/src/router.ts
+++ b/packages/router-core/src/router.ts
@@ -778,6 +778,10 @@ export interface ViewTransitionOptions {
 }
 
 // TODO where is this used? can we remove this?
+/**
+ * Convert an unknown error into a minimal, serializable object.
+ * Includes name and message (and stack in development).
+ */
 export function defaultSerializeError(err: unknown) {
   if (err instanceof Error) {
     const obj = {
@@ -797,6 +801,7 @@ export function defaultSerializeError(err: unknown) {
   }
 }
 
+/** Options for configuring trailing-slash behavior. */
 export const trailingSlashOptions = {
   always: 'always',
   never: 'never',
@@ -806,6 +811,10 @@ export const trailingSlashOptions = {
 export type TrailingSlashOption =
   (typeof trailingSlashOptions)[keyof typeof trailingSlashOptions]
 
+/**
+ * Compute whether path, href or hash changed between previous and current
+ * resolved locations in router state.
+ */
 export function getLocationChangeInfo(routerState: {
   resolvedLocation?: ParsedLocation
   location: ParsedLocation
@@ -2517,8 +2526,10 @@ export class RouterCore<
   }
 }
 
+/** Error thrown when search parameter validation fails. */
 export class SearchParamError extends Error {}
 
+/** Error thrown when path parameter parsing/validation fails. */
 export class PathParamError extends Error {}
 
 const normalize = (str: string) =>
@@ -2527,9 +2538,10 @@ function comparePaths(a: string, b: string) {
   return normalize(a) === normalize(b)
 }
 
-// A function that takes an import() argument which is a function and returns a new function that will
-// proxy arguments from the caller to the imported function, retaining all type
-// information along the way
+/**
+ * Lazily import a module function and forward arguments to it, retaining
+ * parameter and return types for the selected export key.
+ */
 export function lazyFn<
   T extends Record<string, (...args: Array<any>) => any>,
   TKey extends keyof T = 'default',
@@ -2542,6 +2554,7 @@ export function lazyFn<
   }
 }
 
+/** Create an initial RouterState from a parsed location. */
 export function getInitialRouterState(
   location: ParsedLocation,
 ): RouterState<any> {
@@ -2587,6 +2600,10 @@ function validateSearch(validateSearch: AnyValidator, input: unknown): unknown {
   return {}
 }
 
+/**
+ * Build the matched route chain and extract params for a pathname.
+ * Falls back to the root route if no specific route is found.
+ */
 export function getMatchedRoutes<TRouteLike extends RouteLike>({
   pathname,
   routePathname,
diff --git a/packages/router-core/src/scroll-restoration.ts b/packages/router-core/src/scroll-restoration.ts
index cc6432221ce..f2e6fa16ad9 100644
--- a/packages/router-core/src/scroll-restoration.ts
+++ b/packages/router-core/src/scroll-restoration.ts
@@ -34,6 +34,7 @@ function getSafeSessionStorage() {
 }
 
 /** SessionStorage key used to persist scroll restoration state. */
+/** SessionStorage key used to store scroll positions across navigations. */
 export const storageKey = 'tsr-scroll-restoration-v1_3'
 
 const throttle = (fn: (...args: Array<any>) => void, wait: number) => {
@@ -71,6 +72,7 @@ function createScrollRestorationCache(): ScrollRestorationCache | null {
   }
 }
 
+/** In-memory handle to the persisted scroll restoration cache. */
 /** In-memory handle to the persisted scroll restoration cache. */
 export const scrollRestorationCache = createScrollRestorationCache()
 
@@ -81,6 +83,9 @@ export const scrollRestorationCache = createScrollRestorationCache()
  * The `location.href` is used as a fallback to support the use case where the location state is not available like the initial render.
  */
 
+/**
+ * Default scroll restoration cache key: location state key or full href.
+ */
 /**
  * Default scroll restoration cache key: location state key or full href.
  */
diff --git a/packages/router-core/src/searchParams.ts b/packages/router-core/src/searchParams.ts
index f8b9205bebf..e748ac3176e 100644
--- a/packages/router-core/src/searchParams.ts
+++ b/packages/router-core/src/searchParams.ts
@@ -1,6 +1,7 @@
 import { decode, encode } from './qss'
 import type { AnySchema } from './validators'
 
+/** Default `parseSearch` that strips leading '?' and JSON-parses values. */
 /** Default `parseSearch` that strips leading '?' and JSON-parses values. */
 export const defaultParseSearch = parseSearchWith(JSON.parse)
 export const defaultStringifySearch = stringifySearchWith(
diff --git a/packages/router-core/src/ssr/serializer/transformer.ts b/packages/router-core/src/ssr/serializer/transformer.ts
index e20c2e544c3..df86f965edd 100644
--- a/packages/router-core/src/ssr/serializer/transformer.ts
+++ b/packages/router-core/src/ssr/serializer/transformer.ts
@@ -32,6 +32,10 @@ export type UnionizeSerializationAdaptersInput<
   TAdapters extends ReadonlyArray<AnySerializationAdapter>,
 > = TAdapters[number]['~types']['input']
 
+/**
+ * Create a strongly-typed serialization adapter for SSR hydration.
+ * Use to register custom types with the router serializer.
+ */
 export function createSerializationAdapter<
   TInput = unknown,
   TOutput = unknown,
@@ -154,6 +158,7 @@ export interface SerializationAdapterTypes<
 
 export type AnySerializationAdapter = SerializationAdapter<any, any, any>
 
+/** Create a Seroval plugin for server-side serialization only. */
 export function makeSsrSerovalPlugin(
   serializationAdapter: AnySerializationAdapter,
   options: { didRun: boolean },
@@ -182,6 +187,7 @@ export function makeSsrSerovalPlugin(
   })
 }
 
+/** Create a Seroval plugin for client/server symmetric (de)serialization. */
 export function makeSerovalPlugin(
   serializationAdapter: AnySerializationAdapter,
 ): Plugin<any, SerovalNode> {