diff --git a/api/v1/auth.go b/api/v1/auth.go
index 62828eb3..c42e5ab8 100644
--- a/api/v1/auth.go
+++ b/api/v1/auth.go
@@ -33,6 +33,7 @@ type SignUp struct {
 }
 
 func (s *APIV1Service) registerAuthRoutes(g *echo.Group) {
+	// POST /auth/signin - Sign in.
 	g.POST("/auth/signin", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		signin := &SignIn{}
@@ -67,6 +68,7 @@ func (s *APIV1Service) registerAuthRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, user)
 	})
 
+	// POST /auth/signin/sso - Sign in with SSO
 	g.POST("/auth/signin/sso", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		signin := &SSOSignIn{}
@@ -153,6 +155,7 @@ func (s *APIV1Service) registerAuthRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, user)
 	})
 
+	// POST /auth/signup - Sign up a new user.
 	g.POST("/auth/signup", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		signup := &SignUp{}
@@ -218,6 +221,7 @@ func (s *APIV1Service) registerAuthRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, user)
 	})
 
+	// POST /auth/signout - Sign out.
 	g.POST("/auth/signout", func(c echo.Context) error {
 		auth.RemoveTokensAndCookies(c)
 		return c.JSON(http.StatusOK, true)
diff --git a/api/v1/http_getter.go b/api/v1/http_getter.go
index 6d24887c..f98b0fda 100644
--- a/api/v1/http_getter.go
+++ b/api/v1/http_getter.go
@@ -10,6 +10,7 @@ import (
 )
 
 func (*APIV1Service) registerGetterPublicRoutes(g *echo.Group) {
+	// GET /get/httpmeta?url={url} - Get website meta.
 	g.GET("/get/httpmeta", func(c echo.Context) error {
 		urlStr := c.QueryParam("url")
 		if urlStr == "" {
@@ -26,6 +27,7 @@ func (*APIV1Service) registerGetterPublicRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, htmlMeta)
 	})
 
+	// GET /get/image?url={url} - Get image.
 	g.GET("/get/image", func(c echo.Context) error {
 		urlStr := c.QueryParam("url")
 		if urlStr == "" {
diff --git a/api/v1/user.go b/api/v1/user.go
index bb04e090..50ddc4b0 100644
--- a/api/v1/user.go
+++ b/api/v1/user.go
@@ -129,6 +129,7 @@ func (update UpdateUserRequest) Validate() error {
 }
 
 func (s *APIV1Service) registerUserRoutes(g *echo.Group) {
+	// POST /user - Create a new user.
 	g.POST("/user", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		userID, ok := c.Get(getUserIDContextKey()).(int)
@@ -184,6 +185,7 @@ func (s *APIV1Service) registerUserRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, userMessage)
 	})
 
+	// GET /user - List all users.
 	g.GET("/user", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		list, err := s.Store.ListUsers(ctx, &store.FindUser{})
@@ -202,7 +204,7 @@ func (s *APIV1Service) registerUserRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, userMessageList)
 	})
 
-	// GET /api/user/me is used to check if the user is logged in.
+	// GET /user/me - Get current user.
 	g.GET("/user/me", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		userID, ok := c.Get(getUserIDContextKey()).(int)
@@ -233,6 +235,7 @@ func (s *APIV1Service) registerUserRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, userMessage)
 	})
 
+	// GET /user/:id - Get user by id.
 	g.GET("/user/:id", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		id, err := strconv.Atoi(c.Param("id"))
@@ -255,6 +258,7 @@ func (s *APIV1Service) registerUserRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, userMessage)
 	})
 
+	// PUT /user/:id - Update user by id.
 	g.PATCH("/user/:id", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		userID, err := strconv.Atoi(c.Param("id"))
@@ -339,6 +343,7 @@ func (s *APIV1Service) registerUserRoutes(g *echo.Group) {
 		return c.JSON(http.StatusOK, userMessage)
 	})
 
+	// DELETE /user/:id - Delete user by id.
 	g.DELETE("/user/:id", func(c echo.Context) error {
 		ctx := c.Request().Context()
 		currentUserID, ok := c.Get(getUserIDContextKey()).(int)
diff --git a/docs/api/auth.md b/docs/api/auth.md
new file mode 100644
index 00000000..179db4ca
--- /dev/null
+++ b/docs/api/auth.md
@@ -0,0 +1,107 @@
+# Authentication APIs
+
+## Sign In
+
+```
+POST /api/v1/auth/signin
+```
+
+**Request Body**
+
+```json
+{
+  "username": "john",
+  "password": "password123"
+}
+```
+
+**Response**
+
+```json
+{
+  "id": 123,
+  "username": "john",
+  "nickname": "John"
+  // other user fields
+}
+```
+
+**Status Codes**
+
+- 200: Sign in success
+- 400: Invalid request
+- 401: Incorrect credentials
+- 403: User banned
+- 500: Internal server error
+
+## SSO Sign In
+
+```
+POST /api/v1/auth/signin/sso
+```
+
+**Request Body**
+
+```json
+{
+  "identityProviderId": 123,
+  "code": "abc123",
+  "redirectUri": "https://example.com/callback"
+}
+```
+
+**Response**
+
+Same as **Sign In**
+
+**Status Codes**
+
+- 200: Success
+- 400: Invalid request
+- 401: Authentication failed
+- 403: User banned
+- 404: Identity provider not found
+- 500: Internal server error
+
+## Sign Up
+
+```
+POST /api/v1/auth/signup
+```
+
+**Request Body**
+
+```json
+{
+  "username": "mary",
+  "password": "password456"
+}
+```
+
+**Response**
+
+Same as **Sign In**
+
+**Status Codes**
+
+- 200: Sign up success
+- 400: Invalid request
+- 401: Sign up disabled
+- 500: Internal server error
+
+## Sign Out
+
+```
+POST /api/v1/auth/signout
+```
+
+**Response**
+
+```
+true
+```
+
+**Status Codes**
+
+- 200: Success
+- 500: Internal server error
diff --git a/docs/api/how-to.md b/docs/api/how-to.md
new file mode 100644
index 00000000..ebc36283
--- /dev/null
+++ b/docs/api/how-to.md
@@ -0,0 +1,44 @@
+# Guide to Access Memos API with OpenID
+
+Memos API supports using OpenID as the user identifier to access the API.
+
+## What is OpenID
+
+OpenID is a unique identifier assigned by Memos system to each user.
+
+When a user registers or logs in via third-party OAuth through Memos system, the OpenID will be generated automatically.
+
+## How to Get User's OpenID
+
+You can get a user's OpenID through:
+
+- User checks the personal profile page in Memos system
+- Calling Memos API to get user details
+- Retrieving from login API response after successful login
+
+Example:
+
+```
+// GET /api/v1/user/me
+
+{
+  "id": 123,
+  "username": "john",
+  "openId": "8613E04B4FA6603883F05A5E0A5E2517",
+  ...
+}
+```
+
+## How to Use OpenID to Access API
+
+You can access the API on behalf of the user by appending `?openId=xxx` parameter to the API URL.
+
+For example:
+
+```
+curl 'https://demo.usememos.com/api/v1/memo?openId=8613E04B4FA6603883F05A5E0A5E2517' -H 'Content-Type: application/json' --data-raw '{"content":"Hello world!"}'
+```
+
+The above request will create a Memo under the user with OpenID `8613E04B4FA6603883F05A5E0A5E2517`.
+
+OpenID can be used in any API that requires user identity.
diff --git a/docs/api/memo-relation.md b/docs/api/memo-relation.md
new file mode 100644
index 00000000..ff53882e
--- /dev/null
+++ b/docs/api/memo-relation.md
@@ -0,0 +1,67 @@
+# Memo Relation APIs
+
+## Create Memo Relation
+
+```
+POST /api/v1/memo/:memoId/relation
+```
+
+**Request Body**
+
+```json
+{
+  "relatedMemoId": 456,
+  "type": "REFERENCE"
+}
+```
+
+**Response**
+
+```json
+{
+  "memoId": 123,
+  "relatedMemoId": 456,
+  "type": "REFERENCE"
+}
+```
+
+**Status Codes**
+
+- 200: OK
+- 400: Invalid request
+- 500: Internal server error
+
+## Get Memo Relations
+
+```
+GET /api/v1/memo/:memoId/relation
+```
+
+**Response**
+
+```json
+[
+  {
+    "memoId": 123,
+    "relatedMemoId": 456,
+    "type": "REFERENCE"
+  }
+]
+```
+
+**Status Codes**
+
+- 200: OK
+- 500: Internal server error
+
+## Delete Memo Relation
+
+```
+DELETE /api/v1/memo/:memoId/relation/:relatedMemoId/type/:relationType
+```
+
+**Status Codes**
+
+- 200: Deleted
+- 400: Invalid request
+- 500: Internal server error
diff --git a/docs/api/memo-resource.md b/docs/api/memo-resource.md
new file mode 100644
index 00000000..819c57cf
--- /dev/null
+++ b/docs/api/memo-resource.md
@@ -0,0 +1,65 @@
+# Memo Resource APIs
+
+## Bind Resource to Memo
+
+```
+POST /api/v1/memo/:memoId/resource
+```
+
+**Request Body**
+
+```json
+{
+  "resourceId": 123
+}
+```
+
+**Response**
+
+```
+true
+```
+
+**Status Codes**
+
+- 200: OK
+- 400: Invalid request
+- 401: Unauthorized
+- 404: Memo/Resource not found
+- 500: Internal server error
+
+## Get Memo Resources
+
+```
+GET /api/v1/memo/:memoId/resource
+```
+
+**Response**
+
+```json
+[
+  {
+    "id": 123,
+    "filename": "example.png"
+    // other resource fields
+  }
+]
+```
+
+**Status Codes**
+
+- 200: OK
+- 500: Internal server error
+
+## Unbind Resource from Memo
+
+```
+DELETE /api/v1/memo/:memoId/resource/:resourceId
+```
+
+**Status Codes**
+
+- 200: OK
+- 401: Unauthorized
+- 404: Memo/Resource not found
+- 500: Internal server error
diff --git a/docs/api/memo.md b/docs/api/memo.md
new file mode 100644
index 00000000..b54d22f0
--- /dev/null
+++ b/docs/api/memo.md
@@ -0,0 +1,135 @@
+# Memo APIs
+
+## Create Memo
+
+```
+POST /api/v1/memo
+```
+
+**Request Body**
+
+```json
+{
+  "content": "Memo content",
+  "visibility": "PUBLIC",
+  "resourceIdList": [123, 456],
+  "relationList": [{ "relatedMemoId": 789, "type": "LINK" }]
+}
+```
+
+**Response**
+
+```json
+{
+  "id": 1234,
+  "content": "Memo content",
+  "visibility": "PUBLIC"
+  // other fields
+}
+```
+
+**Status Codes**
+
+- 200: Created
+- 400: Invalid request
+- 401: Unauthorized
+- 403: Forbidden to create public memo
+- 500: Internal server error
+
+## Get Memo List
+
+```
+GET /api/v1/memo
+```
+
+**Parameters**
+
+- `creatorId` (optional): Filter by creator ID
+- `visibility` (optional): Filter visibility, `PUBLIC`, `PROTECTED` or `PRIVATE`
+- `pinned` (optional): Filter pinned memo, `true` or `false`
+- `tag` (optional): Filter memo with tag
+- `content` (optional): Search in content
+- `limit` (optional): Limit number of results
+- `offset` (optional): Offset of first result
+
+**Response**
+
+```json
+[
+  {
+    "id": 1234,
+    "content": "Memo 1"
+    // other fields
+  },
+  {
+    "id": 5678,
+    "content": "Memo 2"
+    // other fields
+  }
+]
+```
+
+## Get Memo By ID
+
+```
+GET /api/v1/memo/:memoId
+```
+
+**Response**
+
+```json
+{
+  "id": 1234,
+  "content": "Memo content"
+  // other fields
+}
+```
+
+**Status Codes**
+
+- 200: Success
+- 403: Forbidden for private memo
+- 404: Not found
+- 500: Internal server error
+
+## Update Memo
+
+```
+PATCH /api/v1/memo/:memoId
+```
+
+**Request Body**
+
+```json
+{
+  "content": "Updated content",
+  "visibility": "PRIVATE"
+}
+```
+
+**Response**
+
+Same as **Get Memo By ID**
+
+**Status Codes**
+
+- 200: Updated
+- 400: Invalid request
+- 401: Unauthorized
+- 403: Forbidden
+- 404: Not found
+- 500: Internal server error
+
+## Delete Memo
+
+```
+DELETE /api/v1/memo/:memoId
+```
+
+**Status Codes**
+
+- 200: Deleted
+- 401: Unauthorized
+- 403: Forbidden
+- 404: Not found
+- 500: Internal server error
diff --git a/docs/api/resource.md b/docs/api/resource.md
new file mode 100644
index 00000000..5d09c59c
--- /dev/null
+++ b/docs/api/resource.md
@@ -0,0 +1,130 @@
+# Resource APIs
+
+## Upload Resource
+
+### Upload File
+
+```
+POST /api/v1/resource/blob
+```
+
+**Request Form**
+
+- `file`: Upload file
+
+**Response**
+
+```json
+{
+  "id": 123,
+  "filename": "example.png"
+  // other fields
+}
+```
+
+**Status Codes**
+
+- 200: OK
+- 400: Invalid request
+- 401: Unauthorized
+- 413: File too large
+- 500: Internal server error
+
+### Create Resource
+
+```
+POST /api/v1/resource
+```
+
+**Request Body**
+
+```json
+{
+  "filename": "example.png",
+  "externalLink": "https://example.com/image.png"
+}
+```
+
+**Response**
+
+Same as **Upload File**
+
+**Status Codes**
+
+- 200: OK
+- 400: Invalid request
+- 401: Unauthorized
+- 500: Internal server error
+
+## Get Resource List
+
+```
+GET /api/v1/resource
+```
+
+**Parameters**
+
+- `limit` (optional): Limit number of results
+- `offset` (optional): Offset of first result
+
+**Response**
+
+```json
+[
+  {
+    "id": 123,
+    "filename": "example.png"
+    // other fields
+  },
+  {
+    "id": 456,
+    "filename": "doc.pdf"
+    // other fields
+  }
+]
+```
+
+**Status Codes**
+
+- 200: OK
+- 401: Unauthorized
+- 500: Internal server error
+
+## Update Resource
+
+```
+PATCH /api/v1/resource/:resourceId
+```
+
+**Request Body**
+
+```json
+{
+  "filename": "new_name.png"
+}
+```
+
+**Response**
+
+Same as **Get Resource List**
+
+**Status Codes**
+
+- 200: OK
+- 400: Invalid request
+- 401: Unauthorized
+- 404: Not found
+- 500: Internal server error
+
+## Delete Resource
+
+```
+DELETE /api/v1/resource/:resourceId
+```
+
+**Status Codes**
+
+- 200: Deleted
+- 401: Unauthorized
+- 404: Not found
+- 500: Internal server error
diff --git a/docs/api/tag.md b/docs/api/tag.md
new file mode 100644
index 00000000..4a376193
--- /dev/null
+++ b/docs/api/tag.md
@@ -0,0 +1,84 @@
+# Tag APIs
+
+## Create Tag
+
+```
+POST /api/v1/tag
+```
+
+**Request Body**
+
+```json
+{
+  "name": "python"
+}
+```
+
+**Response**
+
+```
+"python"
+```
+
+**Status Codes**
+
+- 200: Created
+- 400: Invalid request
+- 500: Internal server error
+
+## Get Tag List
+
+```
+GET /api/v1/tag
+```
+
+**Response**
+
+```json
+["python", "golang", "javascript"]
+```
+
+**Status Codes**
+
+- 200: OK
+- 401: Unauthorized
+- 500: Internal server error
+
+## Suggest Tags
+
+```
+GET /api/v1/tag/suggestion
+```
+
+**Response**
+
+```json
+["django", "flask", "numpy"]
+```
+
+**Status Codes**
+
+- 200: OK
+- 401: Unauthorized
+- 500: Internal server error
+
+## Delete Tag
+
+```
+POST /api/v1/tag/delete
+```
+
+**Request Body**
+
+```json
+{
+  "name": "outdated_tag"
+}
+```
+
+**Status Codes**
+
+- 200: Deleted
+- 400: Invalid request
+- 401: Unauthorized
+- 500: Internal server error
diff --git a/docs/api/user.md b/docs/api/user.md
new file mode 100644
index 00000000..768f8ba6
--- /dev/null
+++ b/docs/api/user.md
@@ -0,0 +1,164 @@
+# User APIs
+
+## Create User
+
+```
+POST /api/v1/user
+```
+
+**Request Body**
+
+```json
+{
+  "username": "john",
+  "role": "USER",
+  "email": "john@example.com",
+  "nickname": "John",
+  "password": "password123"
+}
+```
+
+**Response**
+
+```json
+{
+  "id": 123,
+  "username": "john",
+  "role": "USER",
+  "email": "john@example.com",
+  "nickname": "John",
+  "avatarUrl": "",
+  "createdTs": 1596647800,
+  "updatedTs": 1596647800
+}
+```
+
+**Status Codes**
+
+- 200: Success
+- 400: Validation error
+- 401: Unauthorized
+- 403: Forbidden to create host user
+- 500: Internal server error
+
+## Get User List
+
+```
+GET /api/v1/user
+```
+
+**Response**
+
+```json
+[
+  {
+    "id": 123,
+    "username": "john",
+    "role": "USER"
+    // other fields
+  },
+  {
+    "id": 456,
+    "username": "mary",
+    "role": "ADMIN"
+    // other fields
+  }
+]
+```
+
+**Status Codes**
+
+- 200: Success
+- 500: Internal server error
+
+## Get User By ID
+
+```
+GET /api/v1/user/:id
+```
+
+**Response**
+
+```json
+{
+  "id": 123,
+  "username": "john",
+  "role": "USER"
+  // other fields
+}
+```
+
+**Status Codes**
+
+- 200: Success
+- 404: Not found
+- 500: Internal server error
+
+## Update User
+
+```
+PATCH /api/v1/user/:id
+```
+
+**Request Body**
+
+```json
+{
+  "username": "johnny",
+  "email": "johnny@example.com",
+  "nickname": "Johnny",
+  "avatarUrl": "https://avatars.example.com/u=123"
+}
+```
+
+**Response**
+
+```json
+{
+  "id": 123,
+  "username": "johnny",
+  "role": "USER",
+  "email": "johnny@example.com",
+  "nickname": "Johnny",
+  "avatarUrl": "https://avatars.example.com/u=123",
+  "createdTs": 1596647800,
+  "updatedTs": 1596647900
+}
+```
+
+**Status Codes**
+
+- 200: Success
+- 400: Validation error
+- 403: Forbidden
+- 404: Not found
+- 500: Internal server error
+
+## Delete User
+
+```
+DELETE /api/v1/user/:id
+```
+
+**Status Codes**
+
+- 200: Success
+- 403: Forbidden
+- 404: Not found
+- 500: Internal server error
+
+## Get Current User
+
+```
+GET /api/v1/user/me
+```
+
+**Response**
+
+Same as **Get User By ID**
+
+**Status Codes**
+
+- 200: Success
+- 401: Unauthorized
+- 500: Internal server error