diff --git a/docs/_config.yml b/docs/_config.yml
index ee6af41..5c1855a 100644
--- a/docs/_config.yml
+++ b/docs/_config.yml
@@ -5,6 +5,9 @@ description: Minimalist LLM Framework in 100 Lines, Enabling LLMs to Program The
 # Theme settings
 remote_theme: just-the-docs/just-the-docs
 
+# Navigation
+nav_sort: case_sensitive
+
 # Aux links (shown in upper right)
 aux_links:
   "View on GitHub":
@@ -17,10 +20,4 @@ mermaid:
   version: "9.1.3"  # Pick the version you want
   # Default configuration
   config: |
-    directionLR
-
-
-callouts:
-  warning:
-    title: Warning
-    color: red
+    directionLR
\ No newline at end of file
diff --git a/docs/async.md b/docs/async.md
new file mode 100644
index 0000000..c9d265a
--- /dev/null
+++ b/docs/async.md
@@ -0,0 +1,61 @@
+---
+layout: default
+title: "(Advanced) Async"
+parent: "Core Abstraction"
+nav_order: 5
+---
+
+# (Advanced) Async
+
+**Async** Nodes implement `prep_async()`, `exec_async()`, `exec_fallback_async()`, and/or `post_async()`. This is useful for:
+
+1. **prep_async()**  
+   - For *fetching/reading data (files, APIs, DB)* in an I/O-friendly way.
+
+2. **exec_async()**  
+   - Typically used for async LLM calls.
+
+3. **post_async()**  
+   - For *awaiting user feedback*, *coordinating across multi-agents* or any additional async steps after `exec_async()`.
+
+
+**Note**: `AsyncNode` must be wrapped in `AsyncFlow`. `AsyncFlow` can also include regular (sync) nodes.
+
+### Example
+
+```python
+class SummarizeThenVerify(AsyncNode):
+    async def prep_async(self, shared):
+        # Example: read a file asynchronously
+        doc_text = await read_file_async(shared["doc_path"])
+        return doc_text
+
+    async def exec_async(self, prep_res):
+        # Example: async LLM call
+        summary = await call_llm_async(f"Summarize: {prep_res}")
+        return summary
+
+    async def post_async(self, shared, prep_res, exec_res):
+        # Example: wait for user feedback
+        decision = await gather_user_feedback(exec_res)
+        if decision == "approve":
+            shared["summary"] = exec_res
+            return "approve"
+        return "deny"
+
+summarize_node = SummarizeThenVerify()
+final_node = Finalize()
+
+# Define transitions
+summarize_node - "approve" >> final_node
+summarize_node - "deny"    >> summarize_node  # retry
+
+flow = AsyncFlow(start=summarize_node)
+
+async def main():
+    shared = {"doc_path": "document.txt"}
+    await flow.run_async(shared)
+    print("Final Summary:", shared.get("summary"))
+
+asyncio.run(main())
+```
\ No newline at end of file
diff --git a/docs/batch.md b/docs/batch.md
new file mode 100644
index 0000000..b263845
--- /dev/null
+++ b/docs/batch.md
@@ -0,0 +1,107 @@
+---
+layout: default
+title: "Batch"
+parent: "Core Abstraction"
+nav_order: 4
+---
+
+# Batch
+
+**Batch** makes it easier to handle large inputs in one Node or **rerun** a Flow multiple times. Handy for:
+- **Chunk-based** processing (e.g., splitting large texts).
+- **Multi-file** processing.
+- **Iterating** over lists of params (e.g., user queries, documents, URLs).
+
+## 1. BatchNode
+
+A **BatchNode** extends `Node` but changes `prep()` and `exec()`:
+
+- **`prep(shared)`**: returns an **iterable** (e.g., list, generator).
+- **`exec(item)`**: called **once** per item in that iterable.
+- **`post(shared, prep_res, exec_res_list)`**: after all items are processed, receives a **list** of results (`exec_res_list`) and returns an **Action**.
+
+
+### Example: Summarize a Large File
+
+```python
+class MapSummaries(BatchNode):
+    def prep(self, shared):
+        # Suppose we have a big file; chunk it
+        content = shared["data"].get("large_text.txt", "")
+        chunk_size = 10000
+        chunks = [content[i:i+chunk_size] for i in range(0, len(content), chunk_size)]
+        return chunks
+
+    def exec(self, chunk):
+        prompt = f"Summarize this chunk in 10 words: {chunk}"
+        summary = call_llm(prompt)
+        return summary
+
+    def post(self, shared, prep_res, exec_res_list):
+        combined = "\n".join(exec_res_list)
+        shared["summary"]["large_text.txt"] = combined
+        return "default"
+
+map_summaries = MapSummaries()
+flow = Flow(start=map_summaries)
+flow.run(shared)
+```
+
+---
+
+## 2. BatchFlow
+
+A **BatchFlow** runs a **Flow** multiple times, each time with different `params`. Think of it as a loop that replays the Flow for each parameter set.
+
+
+### Example: Summarize Many Files
+
+```python
+class SummarizeAllFiles(BatchFlow):
+    def prep(self, shared):
+        # Return a list of param dicts (one per file)
+        filenames = list(shared["data"].keys())  # e.g., ["file1.txt", "file2.txt", ...]
+        return [{"filename": fn} for fn in filenames]
+
+# Suppose we have a per-file Flow (e.g., load_file >> summarize >> reduce):
+summarize_file = SummarizeFile(start=load_file)
+
+# Wrap that flow into a BatchFlow:
+summarize_all_files = SummarizeAllFiles(start=summarize_file)
+summarize_all_files.run(shared)
+```
+
+### Under the Hood
+1. `prep(shared)` returns a list of param dicts—e.g., `[{filename: "file1.txt"}, {filename: "file2.txt"}, ...]`.
+2. The **BatchFlow** loops through each dict. For each one:
+   - It merges the dict with the BatchFlow’s own `params`.
+   - It calls `flow.run(shared)` using the merged result.
+3. This means the sub-Flow is run **repeatedly**, once for every param dict.
+
+---
+
+## 3. Nested or Multi-Level Batches
+
+You can nest a **BatchFlow** in another **BatchFlow**. For instance:
+- **Outer** batch: returns a list of diretory param dicts (e.g., `{"directory": "/pathA"}`, `{"directory": "/pathB"}`, ...).
+- **Inner** batch: returning a list of per-file param dicts.
+
+At each level, **BatchFlow** merges its own param dict with the parent’s. By the time you reach the **innermost** node, the final `params` is the merged result of **all** parents in the chain. This way, a nested structure can keep track of the entire context (e.g., directory + file name) at once.
+
+```python
+
+class FileBatchFlow(BatchFlow):
+    def prep(self, shared):
+        directory = self.params["directory"]
+        files = [f for f in os.listdir(directory) if f.endswith(".txt")]
+        return [{"filename": f} for f in files]
+
+class DirectoryBatchFlow(BatchFlow):
+    def prep(self, shared):
+        directories = [ "/path/to/dirA", "/path/to/dirB"]
+        return [{"directory": d} for d in directories]
+
+
+inner_flow = FileBatchFlow(start=MapSummaries())
+outer_flow = DirectoryBatchFlow(start=inner_flow)
+```
\ No newline at end of file
diff --git a/docs/communication.md b/docs/communication.md
new file mode 100644
index 0000000..ebba2e2
--- /dev/null
+++ b/docs/communication.md
@@ -0,0 +1,138 @@
+---
+layout: default
+title: "Communication"
+parent: "Core Abstraction"
+nav_order: 3
+---
+
+# Communication
+
+Nodes and Flows **communicate** in two ways:
+
+1. **Shared Store** – A global data structure (often an in-mem dict) that all nodes can read from and write to. Every Node’s `prep()` and `post()` methods receive the **same** `shared` store.  
+2. **Params** – Each node and Flow has a `params` dict assigned by the **parent Flow**. Params mostly serve as identifiers, letting each node/flow know what task it’s assigned.
+
+If you know memory management, **Shared Store** is like a **heap** shared across function calls, while **Params** is like a **stack** assigned by parent function calls.
+
+
+
+> **Why not use other communication models like Message Passing?** *Message passing* works well for simple DAGs, but with *nested graphs* (Flows containing Flows, repeated or cyclic calls), routing messages becomes hard to maintain. A shared store keeps the design simple and easy.
+{: .note }
+
+---
+
+## 1. Shared Store
+
+### Overview
+
+A shared store is typically an in-mem dictionary, like:
+```python
+shared = {"data": {}, "summary": {}, "config": {...}, ...}
+```
+
+It can also contain local file handlers, DB connections, or a combination for persistence. We recommend deciding the data structure or DB schema first based on your app requirements.
+
+### Example
+
+```python
+class LoadData(Node):
+    def prep(self, shared):
+        # Suppose we read from disk or an API
+        shared["data"]["my_file.txt"] = "Some text content"
+        return None
+
+class Summarize(Node):
+    def prep(self, shared):
+        # We can read what LoadData wrote
+        content = shared["data"].get("my_file.txt", "")
+        return content
+
+    def exec(self, prep_res):
+        prompt = f"Summarize: {prep_res}"
+        summary = call_llm(prompt)
+        return summary
+
+    def post(self, shared, prep_res, exec_res):
+        shared["summary"]["my_file.txt"] = exec_res
+        return "default"
+
+load_data = LoadData()
+summarize = Summarize()
+load_data >> summarize
+flow = Flow(start=load_data)
+
+shared = {}
+flow.run(shared)
+```
+
+Here:
+- `LoadData` writes to `shared["data"]`.
+- `Summarize` reads from the same location.  
+No special data-passing—just the same `shared` object.
+
+---
+
+## 2. Params
+
+**Params** let you store *per-Node* or *per-Flow* config that doesn't need to live in the shared store. They are:
+- **Immutable** during a Node’s run cycle (i.e., they don’t change mid-`prep`, `exec`, `post`).
+- **Set** via `set_params()`.
+- **Cleared** and updated each time a parent Flow calls it.
+
+
+> Only set the uppermost Flow params because others will be overwritten by the parent Flow. If you need to set child node params, see [Batch](./batch.md).
+{: .warning }
+
+Typically, **Params** are identifiers (e.g., file name, page number). Use them to fetch the task you assigned or write to a specific part of the shared store.
+
+### Example
+
+```python
+# 1) Create a Node that uses params
+class SummarizeFile(Node):
+    def prep(self, shared):
+        # Access the node's param
+        filename = self.params["filename"]
+        return shared["data"].get(filename, "")
+
+    def exec(self, prep_res):
+        prompt = f"Summarize: {prep_res}"
+        return call_llm(prompt)
+
+    def post(self, shared, prep_res, exec_res):
+        filename = self.params["filename"]
+        shared["summary"][filename] = exec_res
+        return "default"
+
+# 2) Set params
+node = SummarizeFile()
+
+# 3) Set Node params directly (for testing)
+node.set_params({"filename": "doc1.txt"})
+node.run(shared)
+
+# 4) Create Flow
+flow = Flow(start=node)
+
+# 5) Set Flow params (overwrites node params)
+flow.set_params({"filename": "doc2.txt"})
+flow.run(shared)  # The node summarizes doc2, not doc1
+```
+
+---
+
+## 3. Shared Store vs. Params
+
+Think of the **Shared Store** like a heap and **Params** like a stack.
+
+- **Shared Store**:
+  - Public, global.
+  - You can design and populate ahead, e.g., for the input to process.
+  - Great for data results, large content, or anything multiple nodes need.
+  - Keep it tidy—structure it carefully (like a mini schema).
+
+- **Params**:
+  - Local, ephemeral.
+  - Passed in by parent Flows. You should only set it for the uppermost flow.
+  - Perfect for small values like filenames or numeric IDs.
+  - Do **not** persist across different nodes and are reset.
\ No newline at end of file
diff --git a/docs/core_abstraction.md b/docs/core_abstraction.md
new file mode 100644
index 0000000..6043574
--- /dev/null
+++ b/docs/core_abstraction.md
@@ -0,0 +1,6 @@
+---
+layout: default
+title: "Core Abstraction"
+nav_order: 2
+has_children: true
+---
\ No newline at end of file
diff --git a/docs/flow.md b/docs/flow.md
new file mode 100644
index 0000000..6ac6208
--- /dev/null
+++ b/docs/flow.md
@@ -0,0 +1,171 @@
+---
+layout: default
+title: "Flow"
+parent: "Core Abstraction"
+nav_order: 2
+---
+
+# Flow
+
+A **Flow** orchestrates how Nodes connect and run, based on **Actions** returned from each Node’s `post()` method. You can chain Nodes in a sequence or create branching logic depending on the **Action** string.
+
+## 1. Action-based Transitions
+
+Each Node's `post(shared, prep_res, exec_res)` method returns an **Action** string. By default, if `post()` doesn't explicitly return anything, we treat that as `"default"`.
+
+You define transitions with the syntax:
+
+1. Basic default transition: `node_a >> node_b`
+  This means if `node_a.post()` returns `"default"` (or `None`), go to `node_b`. 
+  (Equivalent to `node_a - "default" >> node_b`)
+
+2. Named action transition: `node_a - "action_name" >> node_b`
+  This means if `node_a.post()` returns `"action_name"`, go to `node_b`.
+
+It’s possible to create loops, branching, or multi-step flows.
+
+## 2. Creating a Flow
+
+A **Flow** begins with a **start** node (or flow). You call `Flow(start=some_node)` to specify the entry point. When you call `flow.run(shared)`, it executes the first node, looks at its `post()` return Action, follows the corresponding transition, and continues until there’s no next node or you explicitly stop.
+
+### Example: Simple Sequence
+
+Here’s a minimal flow of two nodes in a chain:
+
+```python
+node_a >> node_b
+flow = Flow(start=node_a)
+flow.run(shared)
+```
+
+- When you run the flow, it executes `node_a`.  
+- Suppose `node_a.post()` returns `"default"`.  
+- The flow then sees `"default"` Action is linked to `node_b` and runs `node_b`.  
+- If `node_b.post()` returns `"default"` but we didn’t define `node_b >> something_else`, the flow ends there.
+
+### Example: Branching & Looping
+
+Here's a simple expense approval flow that demonstrates branching and looping. The `ReviewExpense` node can return three possible Actions:
+
+- `"approved"`: expense is approved, move to payment processing
+- `"needs_revision"`: expense needs changes, send back for revision 
+- `"rejected"`: expense is denied, finish the process
+
+We can wire them like this:
+
+```python
+# Define the flow connections
+review - "approved" >> payment        # If approved, process payment
+review - "needs_revision" >> revise   # If needs changes, go to revision
+review - "rejected" >> finish           # If rejected, finish the process
+
+revise >> review   # After revision, go back for another review
+payment >> finish     # After payment, finish the process
+
+flow = Flow(start=review)
+```
+
+Let's see how it flows:
+
+1. If `review.post()` returns `"approved"`, the expense moves to `payment` node
+2. If `review.post()` returns `"needs_revision"`, it goes to `revise` node, which then loops back to `review`
+3. If `review.post()` returns `"rejected"`, it moves to `finish` node and stops
+
+```mermaid
+flowchart TD
+    review[Review Expense] -->|approved| payment[Process Payment]
+    review -->|needs_revision| revise[Revise Report]
+    review -->|rejected| finish[Finish Process]
+
+    revise --> review
+    payment --> finish
+```
+
+### Running Individual Nodes vs. Running a Flow
+
+- `node.run(shared)`: Just runs that node alone (calls `prep()`, `exec()`, `post()`), returns an Action. 
+- `flow.run(shared)`: Executes from the start node, follows Actions to the next node, and so on until the flow can’t continue (no next node or no next Action).
+
+
+> node.run(shared) **does not** proceed automatically to the successor and may use incorrect parameters.
+> This is mainly for debugging or testing a single node.
+> Always use `flow.run(...)` in production to ensure the full pipeline runs correctly.
+{: .warning }
+
+## 3. Nested Flows
+
+A **Flow** can act like a Node, which enables powerful composition patterns. This means you can:
+
+1. Use a Flow as a Node within another Flow's transitions.  
+2. Combine multiple smaller Flows into a larger Flow for reuse.  
+3. Node `params` will be a merging of **all** parents' `params`.
+
+### Basic Flow Nesting
+
+Here's how to connect a flow to another node:
+
+```python
+# Create a sub-flow
+node_a >> node_b
+subflow = Flow(start=node_a)
+
+# Connect it to another node
+subflow >> node_c
+
+# Create the parent flow
+parent_flow = Flow(start=subflow)
+```
+
+When `parent_flow.run()` executes:
+1. It starts `subflow`
+2. `subflow` runs through its nodes (`node_a` then `node_b`)
+3. After `subflow` completes, execution continues to `node_c`
+
+### Example: Order Processing Pipeline
+
+Here's a practical example that breaks down order processing into nested flows:
+
+```python
+# Payment processing sub-flow
+validate_payment >> process_payment >> payment_confirmation
+payment_flow = Flow(start=validate_payment)
+
+# Inventory sub-flow
+check_stock >> reserve_items >> update_inventory
+inventory_flow = Flow(start=check_stock)
+
+# Shipping sub-flow
+create_label >> assign_carrier >> schedule_pickup
+shipping_flow = Flow(start=create_label)
+
+# Connect the flows into a main order pipeline
+payment_flow >> inventory_flow >> shipping_flow
+
+# Create the master flow
+order_pipeline = Flow(start=payment_flow)
+
+# Run the entire pipeline
+order_pipeline.run(shared_data)
+```
+
+This creates a clean separation of concerns while maintaining a clear execution path:
+
+```mermaid
+flowchart LR
+    subgraph order_pipeline[Order Pipeline]
+        subgraph paymentFlow["Payment Flow"]
+            A[Validate Payment] --> B[Process Payment] --> C[Payment Confirmation]
+        end
+
+        subgraph inventoryFlow["Inventory Flow"]
+            D[Check Stock] --> E[Reserve Items] --> F[Update Inventory]
+        end
+
+        subgraph shippingFlow["Shipping Flow"]
+            G[Create Label] --> H[Assign Carrier] --> I[Schedule Pickup]
+        end
+
+        paymentFlow --> inventoryFlow
+        inventoryFlow --> shippingFlow
+    end
+```
diff --git a/docs/index.md b/docs/index.md
index bc50f0a..7099c1f 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -4,14 +4,60 @@ title: "Home"
 nav_order: 1
 ---
 
-> **Heads up!** This is a note callout.
+# Mini LLM Flow
+
+A [100-line](https://github.com/zachary62/miniLLMFlow/blob/main/minillmflow/__init__.py) minimalist LLM framework for *Agents, Task Decomposition, RAG, etc*.
+
+
+We model the LLM workflow as a **Nested Directed Graph**:
+- **Nodes** handle simple (LLM) tasks.
+- Nodes connect through **Actions** (labeled edges) for *Agents*.  
+- **Flows** orchestrate a directed graph of Nodes for *Task Decomposition*.
+- A Flow can be used as a Node (for **Nesting**).
+- **Batch** Nodes/Flows for data-intensive tasks.
+- **Async** Nodes/Flows allow waits or **Parallel** execution
+
+
+<div align="center">
+  <img src="https://github.com/zachary62/miniLLMFlow/blob/main/assets/minillmflow.jpg?raw=true" width="400"/>
+</div>
+
+
 {: .note }
+> Have questions? Chat with [AI Assistant](https://chatgpt.com/g/g-677464af36588191b9eba4901946557b-mini-llm-flow-assistant)
+
+
+
+## Core Abstraction
+
+- [Node](./node.md)
+- [Flow](./flow.md)
+- [Communication](./communication.md)
+- [Batch](./batch.md)
+- [(Advanced) Async](./async.md)
+- [(Advanced) Parallel](./parallel.md)
+
+## Low-Level Details
+
+- [LLM Wrapper](./llm.md)
+- [Tool](./tool.md)
 
-> This is a tip callout.
-{: .tip }
 
-> This is a warning callout.
 {: .warning }
+> We do not provide built-in implementation for low-level details. Example implementations are provided as reference.
 
-> This is an important callout.
-{: .important }
\ No newline at end of file
+
+## High-Level Paradigm
+
+- [Structured Output](./structure.md)
+- Task Decomposition
+- Map Reduce
+- RAG
+- Chat Memory
+- Agent
+- Multi-Agent
+- Evaluation
+
+## Example Projects
+
+- Coming soon ... 
diff --git a/docs/llm.md b/docs/llm.md
new file mode 100644
index 0000000..789cd06
--- /dev/null
+++ b/docs/llm.md
@@ -0,0 +1,69 @@
+---
+layout: default
+title: "LLM Wrapper"
+parent: "Preparation"
+nav_order: 1
+---
+
+# LLM Wrappers  
+
+We **don't** provide built-in LLM wrappers. Instead, please implement your own, for example by asking an assistant like ChatGPT or Claude. If you ask ChatGPT to "implement a `call_llm` function that takes a prompt and returns the LLM response," you shall get something like:
+
+```python
+def call_llm(prompt):
+    from openai import OpenAI
+    # Set the OpenAI API key (use environment variables, etc.)
+    client = OpenAI(api_key="YOUR_API_KEY_HERE")
+    r = client.chat.completions.create(
+        model="gpt-4",
+        messages=[{"role": "user", "content": prompt}]
+    )
+    return r.choices[0].message.content
+
+# Example usage
+call_llm("How are you?")
+```
+
+## Improvements
+Feel free to enhance your `call_llm` function as needed. Here are examples:
+
+- Handle chat history:
+
+```python
+def call_llm(messages):
+    from openai import OpenAI
+    client = OpenAI(api_key="YOUR_API_KEY_HERE")
+    r = client.chat.completions.create(
+        model="gpt-4",
+        messages=messages
+    )
+    return r.choices[0].message.content
+```
+
+- Add in-memory caching:
+
+```python
+from functools import lru_cache
+
+@lru_cache(maxsize=1000)
+def call_llm(prompt):
+    # Your implementation here
+    pass
+```
+
+- Enable logging:
+
+```python
+def call_llm(prompt):
+    import logging
+    logging.info(f"Prompt: {prompt}")
+    response = ... # Your implementation here
+    logging.info(f"Response: {response}")
+    return response
+```
+
+## Why Not Provide Built-in LLM Wrappers?
+I believe it is a **bad practice** to provide LLM-specific implementations in a general framework:
+- **LLM APIs change frequently**. Hardcoding them makes maintenance a nighmare.
+- You may need **flexibility** to switch vendors, use fine-tuned models, or deploy local LLMs.
+- You may need **optimizations** like prompt caching, request batching, or response streaming.
diff --git a/docs/node.md b/docs/node.md
new file mode 100644
index 0000000..aeaa61e
--- /dev/null
+++ b/docs/node.md
@@ -0,0 +1,95 @@
+---
+layout: default
+title: "Node"
+parent: "Core Abstraction"
+nav_order: 1
+---
+
+# Node
+
+A **Node** is the smallest building block of Mini LLM Flow. Each Node has 3 steps:
+
+1. **`prep(shared)`**  
+   - Reads and preprocesses data from the `shared` store for LLMs.
+   - Examples: *query DB, read files, or serialize data into a string*.
+   - Returns `prep_res`, which will be passed to both `exec()` and `post()`.
+
+2. **`exec(prep_res)`**  
+   - The main execution step where the LLM is called.
+   - Optionally has built-in retry and error handling (below).
+   - ⚠️ If retry enabled, ensure implementation is idempotent.
+   - Returns `exec_res`, which is passed to `post()`.
+
+3. **`post(shared, prep_res, exec_res)`**  
+   - Writes results back to the `shared` store or decides the next action.  
+   - Examples: *finalize outputs, trigger next steps, or log results*.
+   - Returns a **string** to specify the next action (`"default"` if nothing or `None` is returned).
+
+
+> All 3 steps are optional. For example, you might only need to run the Prep without calling the LLM.
+{: .note }
+
+
+## Fault Tolerance & Retries
+
+Nodes in Mini LLM Flow can **retry** execution if `exec()` raises an exception. You control this via two parameters when you create the Node:
+
+- `max_retries` (int): How many times to try running `exec()`. The default is `1`, which means **no** retry.
+- `wait` (int): The time to wait (in **seconds**) before each retry attempt. By default, `wait=0` (i.e., no waiting). Increasing this is helpful when you encounter rate-limits or quota errors from your LLM provider and need to back off.
+
+```python 
+my_node = SummarizeFile(max_retries=3, wait=10)
+```
+
+When an exception occurs in `exec()`, the Node automatically retries until:
+
+- It either succeeds, or
+- The Node has retried `max_retries - 1` times already and fails on the last attempt.
+
+### Graceful Fallback
+
+If you want to **gracefully handle** the error rather than raising it, you can override:
+
+```python 
+def exec_fallback(self, shared, prep_res, exc):
+    raise exc
+```
+
+By default, it just re-raises `exc`. But you can return a fallback result instead. 
+That fallback result becomes the `exec_res` passed to `post()`.
+
+## Example
+
+```python 
+class SummarizeFile(Node):
+    def prep(self, shared):
+        filename = self.params["filename"]
+        return shared["data"][filename]
+
+    def exec(self, prep_res):
+        if not prep_res:
+            raise ValueError("Empty file content!")
+        prompt = f"Summarize this text in 10 words: {prep_res}"
+        summary = call_llm(prompt)  # might fail
+        return summary
+
+    def exec_fallback(self, shared, prep_res, exc):
+        # Provide a simple fallback instead of crashing
+        return "There was an error processing your request."
+
+    def post(self, shared, prep_res, exec_res):
+        filename = self.params["filename"]
+        shared["summary"][filename] = exec_res
+        # Return "default" by not returning anything
+
+summarize_node = SummarizeFile(max_retries=3)
+
+# Run the node standalone for testing (calls prep->exec->post).
+# If exec() fails, it retries up to 3 times before calling exec_fallback().
+summarize_node.set_params({"filename": "test_file.txt"})
+action_result = summarize_node.run(shared)
+
+print("Action returned:", action_result)  # Usually "default"
+print("Summary stored:", shared["summary"].get("test_file.txt"))
+```  
+
diff --git a/docs/paradigm.md b/docs/paradigm.md
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--- /dev/null
+++ b/docs/paradigm.md
@@ -0,0 +1,6 @@
+---
+layout: default
+title: "Paradigm"
+nav_order: 4
+has_children: true
+---
\ No newline at end of file
diff --git a/docs/parallel.md b/docs/parallel.md
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--- /dev/null
+++ b/docs/parallel.md
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+---
+layout: default
+title: "(Advanced) Parallel"
+parent: "Core Abstraction"
+nav_order: 6
+---
+
+# (Advanced) Parallel
+
+**Parallel** Nodes and Flows let you run multiple **Async** Nodes and Flows  **concurrently**—for example, summarizing multiple texts at once. This can improve performance by overlapping I/O and compute. 
+
+## AsyncParallelBatchNode
+
+Like **AsyncBatchNode**, but run `exec_async()` in **parallel**:
+
+```python
+class ParallelSummaries(AsyncParallelBatchNode):
+    async def prep_async(self, shared):
+        # e.g., multiple texts
+        return shared["texts"]
+
+    async def exec_async(self, text):
+        prompt = f"Summarize: {text}"
+        return await call_llm_async(prompt)
+
+    async def post_async(self, shared, prep_res, exec_res_list):
+        shared["summary"] = "\n\n".join(exec_res_list)
+        return "default"
+
+node = ParallelSummaries()
+flow = AsyncFlow(start=node)
+```
+
+## AsyncParallelBatchFlow
+
+Parallel version of **BatchFlow**. Each iteration of the sub-flow runs **concurrently** using different parameters:
+
+```python
+class SummarizeMultipleFiles(AsyncParallelBatchFlow):
+    async def prep_async(self, shared):
+        return [{"filename": f} for f in shared["files"]]
+
+sub_flow = AsyncFlow(start=LoadAndSummarizeFile())
+parallel_flow = SummarizeMultipleFiles(start=sub_flow)
+await parallel_flow.run_async(shared)
+```
+
+## Best Practices
+
+- **Ensure Tasks Are Independent**: If each item depends on the output of a previous item, **do not** parallelize.
+
+- **Beware of Rate Limits**: Parallel calls can **quickly** trigger rate limits on LLM services. You may need a **throttling** mechanism (e.g., semaphores or sleep intervals).
+
+- **Consider Single-Node Batch APIs**: Some LLMs offer a **batch inference** API where you can send multiple prompts in a single call. This is more complex to implement but can be more efficient than launching many parallel requests and mitigates rate limits.
diff --git a/docs/preparation.md b/docs/preparation.md
new file mode 100644
index 0000000..9e8cbf9
--- /dev/null
+++ b/docs/preparation.md
@@ -0,0 +1,6 @@
+---
+layout: default
+title: "Preparation"
+nav_order: 3
+has_children: true
+---
\ No newline at end of file
diff --git a/docs/structure.md b/docs/structure.md
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--- /dev/null
+++ b/docs/structure.md
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+---
+layout: default
+title: "Structured Output"
+parent: "Paradigm"
+nav_order: 1
+---
+
+# Structured Output
+
+In many use cases, you may want the LLM to output a specific structure, such as a list or a dictionary with predefined keys.
+
+There are several approaches to achieve a structured output:
+- **Prompting** the LLM to strictly return a defined structure.
+- Using LLMs that natively support **schema enforcement**.
+- **Post-processing** the LLM’s response to extract structured content.
+
+In practice, **Prompting** is simple and reliable for modern LLMs.
+
+### Example Use Cases
+
+- Extracting Key Information 
+
+```yaml
+product:
+  name: Widget Pro
+  price: 199.99
+  description: |
+    A high-quality widget designed for professionals.
+    Recommended for advanced users.
+```
+
+- Summarizing Documents into Bullet Points
+
+```yaml
+summary:
+  - This product is easy to use.
+  - It is cost-effective.
+  - Suitable for all skill levels.
+```
+
+- Generating Configuration Files
+
+```yaml
+server:
+  host: 127.0.0.1
+  port: 8080
+  ssl: true
+```
+
+## Prompt Engineering
+
+When prompting the LLM to produce **structured** output:
+1. **Wrap** the structure in code fences (e.g., ` ```yaml`).
+2. **Validate** that all required fields exist (and let `Node` handles retry).
+
+### Example Text Summarization
+
+```python
+class SummarizeNode(Node):
+    def exec(self, prep_res):
+        # Suppose `prep_res` is the text to summarize.
+        prompt = f"""
+Please summarize the following text as YAML, with exactly 3 bullet points
+
+{prep_res}
+
+Now, output:
+```yaml
+summary:
+  - bullet 1
+  - bullet 2
+  - bullet 3
+```"""
+        response = call_llm(prompt)
+        yaml_str = response.split("```yaml")[1].split("```")[0].strip()
+
+        import yaml
+        structured_result = yaml.safe_load(yaml_str)
+
+        assert "summary" in structured_result
+        assert isinstance(structured_result["summary"], list)
+
+        return structured_result
+```
+
+### Why YAML instead of JSON?
+
+Current LLMs struggle with escaping. YAML is easier with strings since they don’t always need quotes.
+
+**In JSON**  
+
+```json
+{
+  "dialogue": "Alice said: \"Hello Bob.\\nHow are you?\\nI am good.\""
+}
+```
+
+- Every double quote inside the string must be escaped with `\"`.
+- Each newline in the dialogue must be represented as `\n`.
+
+**In YAML**  
+
+```yaml
+dialogue: |
+  Alice said: "Hello Bob.
+  How are you?
+  I am good."
+```
+
+- No need to escape interior quotes—just place the entire text under a block literal (`|`).
+- Newlines are naturally preserved without needing `\n`.
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diff --git a/docs/tool.md b/docs/tool.md
new file mode 100644
index 0000000..a0256b0
--- /dev/null
+++ b/docs/tool.md
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+---
+layout: default
+title: "Tool"
+parent: "Preparation"
+nav_order: 2
+---
+
+# Tool
+
+Similar to LLM wrappers, we **don't** provide built-in tools. Here, we recommend some *minimal* (and incomplete) implementations of commonly used tools. These examples can serve as a starting point for your own tooling.
+
+---
+
+
+## 1. Embedding Calls
+
+```python
+def get_embedding(text):
+    import openai
+    # Set your API key elsewhere, e.g., environment variables
+    r = openai.Embedding.create(
+        model="text-embedding-ada-002",
+        input=text
+    )
+    return r["data"][0]["embedding"]
+```
+
+---
+
+## 2. Vector Database (Faiss)
+
+```python
+import faiss
+import numpy as np
+
+def create_index(embeddings):
+    dim = len(embeddings[0])
+    index = faiss.IndexFlatL2(dim)
+    index.add(np.array(embeddings).astype('float32'))
+    return index
+
+def search_index(index, query_embedding, top_k=5):
+    D, I = index.search(
+        np.array([query_embedding]).astype('float32'), 
+        top_k
+    )
+    return I, D
+```
+
+---
+
+## 3. Local Database
+
+```python
+import sqlite3
+
+def execute_sql(query):
+    conn = sqlite3.connect("mydb.db")
+    cursor = conn.cursor()
+    cursor.execute(query)
+    result = cursor.fetchall()
+    conn.commit()
+    conn.close()
+    return result
+```
+
+---
+
+## 4. Python Function Execution
+
+```python
+def run_code(code_str):
+    env = {}
+    exec(code_str, env)
+    return env
+```
+
+---
+
+## 5. PDF Extraction
+
+```python
+def extract_text_from_pdf(file_path):
+    import PyPDF2
+    pdfFileObj = open(file_path, "rb")
+    reader = PyPDF2.PdfReader(pdfFileObj)
+    text = ""
+    for page in reader.pages:
+        text += page.extract_text()
+    pdfFileObj.close()
+    return text
+```
+
+---
+
+## 6. Web Crawling
+
+```python
+def crawl_web(url):
+    import requests
+    from bs4 import BeautifulSoup
+    html = requests.get(url).text
+    soup = BeautifulSoup(html, "html.parser")
+    return soup.title.string, soup.get_text()
+```
+
+---
+
+## 7. Basic Search (SerpAPI example)
+
+```python
+def search_google(query):
+    import requests
+    params = {
+        "engine": "google",
+        "q": query,
+        "api_key": "YOUR_API_KEY"
+    }
+    r = requests.get("https://serpapi.com/search", params=params)
+    return r.json()
+```
+
+---
+
+
+## 8. Audio Transcription (OpenAI Whisper)
+
+```python
+def transcribe_audio(file_path):
+    import openai
+    audio_file = open(file_path, "rb")
+    transcript = openai.Audio.transcribe("whisper-1", audio_file)
+    return transcript["text"]
+```
+
+---
+
+## 9. Text-to-Speech (TTS)
+
+```python
+def text_to_speech(text):
+    import pyttsx3
+    engine = pyttsx3.init()
+    engine.say(text)
+    engine.runAndWait()
+```
+
+---
+
+## 10. Sending Email
+
+```python
+def send_email(to_address, subject, body, from_address, password):
+    import smtplib
+    from email.mime.text import MIMEText
+
+    msg = MIMEText(body)
+    msg["Subject"] = subject
+    msg["From"] = from_address
+    msg["To"] = to_address
+
+    with smtplib.SMTP_SSL("smtp.gmail.com", 465) as server:
+        server.login(from_address, password)
+        server.sendmail(from_address, [to_address], msg.as_string())
+```
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