diff --git a/README.md b/README.md
index 0b23753f..e5dcf113 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,9 @@
 # Numaflow Golang SDK
 
-This SDK provides the interfaces to implement [Numaflow](https://github.com/numaproj/numaflow) User Defined Sources, Functions or Sinks in Golang.
-- Implement [User Defined Sources](TODO-PLACEHOLDER)
+This SDK provides the interfaces to implement [Numaflow](https://github.com/numaproj/numaflow) User Defined Sources,
+Source Transformer, Functions, Sinks or SideInputs in Golang.
+- Implement [User Defined Sources](https://pkg.go.dev/github.com/numaproj/numaflow-go/pkg/sourcer)
+- Implement [User Defined Source Transformers](https://pkg.go.dev/github.com/numaproj/numaflow-go/pkg/sourcetransformer)
 - Implement [User Defined Functions](https://pkg.go.dev/github.com/numaproj/numaflow-go/pkg/function)
-- Implement [User Defined Sinks](https://pkg.go.dev/github.com/numaproj/numaflow-go/pkg/sink)
\ No newline at end of file
+- Implement [User Defined Sinks](https://pkg.go.dev/github.com/numaproj/numaflow-go/pkg/sink)
+- Implement [User Defined SideInputs](https://pkg.go.dev/github.com/numaproj/numaflow-go/pkg/sideinput)
\ No newline at end of file
diff --git a/pkg/sourcer/doc.go b/pkg/sourcer/doc.go
index f6e0d59c..d074f682 100644
--- a/pkg/sourcer/doc.go
+++ b/pkg/sourcer/doc.go
@@ -1,2 +1,104 @@
 // Package sourcer implements the server code for User Defined Sourcer in golang.
+//
+// Example:
+/*
+    import (
+	"context"
+	"log"
+	"strconv"
+	"sync"
+	"time"
+
+	"github.com/numaproj/numaflow-go/pkg/sourcer"
+	sourcesdk "github.com/numaproj/numaflow-go/pkg/sourcer"
+	)
+
+	// A simple example of a user-defined source.
+	// The source maintains an array of messages and implements the `Read()`, `Ack()`, and `Pending()` methods.
+
+	// The `Read(x)` method returns the next x number of messages in the array.
+	// The `Ack()` method acknowledges the last batch of messages returned by `Read()`.
+	// The `Pending()` method returns 0 to indicate that the simple source always has 0 pending messages.
+
+	func main() {
+		simpleSource := NewSimpleSource()
+		err := sourcer.NewServer(simpleSource).Start(context.Background())
+		if err != nil {
+			log.Panic("Failed to start source server : ", err)
+		}
+	}
+
+	// SimpleSource is a simple source implementation.
+	type SimpleSource struct {
+		readIdx  int64
+		toAckSet map[int64]struct{}
+		lock     *sync.Mutex
+	}
+
+	func NewSimpleSource() *SimpleSource {
+		return &SimpleSource{
+			readIdx:  0,
+			toAckSet: make(map[int64]struct{}),
+			lock:     new(sync.Mutex),
+		}
+	}
+
+	// Pending returns the number of pending records.
+	func (s *SimpleSource) Pending(_ context.Context) int64 {
+		// The simple source always returns zero to indicate no pending records.
+		return 0
+	}
+
+	// Read reads messages from the source and sends the messages to the message channel.
+	// If the read request is timed out, the function returns without reading new data.
+	// Right after reading a message, the function marks the offset as to be acked.
+	func (s *SimpleSource) Read(_ context.Context, readRequest sourcesdk.ReadRequest, messageCh chan<- sourcesdk.Message) {
+		// Handle the timeout specification in the read request.
+		ctx, cancel := context.WithTimeout(context.Background(), readRequest.TimeOut())
+		defer cancel()
+
+		// If we have un-acked data, we return without reading any new data.
+		if len(s.toAckSet) > 0 {
+			return
+		}
+
+		// Read the data from the source and send the data to the message channel.
+		for i := 0; uint64(i) < readRequest.Count(); i++ {
+			select {
+			case <-ctx.Done():
+				// If the context is done, the read request is timed out.
+				return
+			default:
+				s.lock.Lock()
+				// Otherwise, we read the data from the source and send the data to the message channel.
+				offsetValue := serializeOffset(s.readIdx)
+				messageCh <- sourcesdk.NewMessage(
+					[]byte(strconv.FormatInt(s.readIdx, 10)),
+					sourcesdk.NewOffset(offsetValue, "0"),
+					time.Now())
+				// Mark the offset as to be acked, and increment the read index.
+				s.toAckSet[s.readIdx] = struct{}{}
+				s.readIdx++
+				s.lock.Unlock()
+			}
+		}
+	}
+
+	// Ack acknowledges the data from the source.
+	func (s *SimpleSource) Ack(_ context.Context, request sourcesdk.AckRequest) {
+		for _, offset := range request.Offsets() {
+			delete(s.toAckSet, deserializeOffset(offset.Value()))
+		}
+	}
+
+	func serializeOffset(idx int64) []byte {
+		return []byte(strconv.FormatInt(idx, 10))
+	}
+
+	func deserializeOffset(offset []byte) int64 {
+		idx, _ := strconv.ParseInt(string(offset), 10, 64)
+		return idx
+	}
+*/
+
 package sourcer
diff --git a/pkg/sourcetransformer/doc.go b/pkg/sourcetransformer/doc.go
index 8bcec8e4..9cbf7d36 100644
--- a/pkg/sourcetransformer/doc.go
+++ b/pkg/sourcetransformer/doc.go
@@ -1,4 +1,4 @@
-// Package source implements the server code for Source Transformer in golang.
+// Package sourcetransformer implements the server code for Source Transformer in golang.
 //
 // Example Transform (extracting event time from the datum payload)
 // Transform includes both Map and EventTime assignment functionalities.