diff --git a/ctclient/client.go b/ctclient/client.go
index d9b2d3a..cbf1c9b 100644
--- a/ctclient/client.go
+++ b/ctclient/client.go
@@ -22,6 +22,8 @@ import (
 	"net/http"
 	"net/url"
 	"time"
+
+	"software.sslmate.com/src/certspotter/cttypes"
 )
 
 var UserAgent = ""
@@ -108,3 +110,55 @@ func getRoots(ctx context.Context, httpClient *http.Client, logURL *url.URL) ([]
 	}
 	return parsedResponse.Certificates, nil
 }
+
+func addChainOrPreChain(ctx context.Context, httpClient *http.Client, logURL *url.URL, isPreChain bool, chain [][]byte) (*cttypes.SignedCertificateTimestamp, error) {
+	var endpoint string
+	if isPreChain {
+		endpoint = "/ct/v1/add-pre-chain"
+	} else {
+		endpoint = "/ct/v1/add-chain"
+	}
+	fullURL := logURL.JoinPath(endpoint).String()
+
+	requestBody, err := json.Marshal(struct {
+		Chain [][]byte `json:"chain"`
+	}{
+		Chain: chain,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	request, err := http.NewRequestWithContext(ctx, http.MethodPost, fullURL, bytes.NewReader(requestBody))
+	if err != nil {
+		return nil, err
+	}
+	request.Header.Set("User-Agent", UserAgent)
+	request.Header.Set("Content-Type", "application/json")
+
+	if httpClient == nil {
+		httpClient = defaultHTTPClient
+	}
+
+	response, err := httpClient.Do(request)
+	if err != nil {
+		return nil, err
+	}
+
+	responseBody, err := io.ReadAll(response.Body)
+	response.Body.Close()
+	if err != nil {
+		return nil, fmt.Errorf("Post %q: error reading response: %w", fullURL, err)
+	}
+
+	if response.StatusCode != 200 {
+		return nil, fmt.Errorf("Post %q: %s (%q)", fullURL, response.Status, bytes.TrimSpace(responseBody))
+	}
+
+	sct := new(cttypes.SignedCertificateTimestamp)
+	if err := json.Unmarshal(responseBody, sct); err != nil {
+		return nil, fmt.Errorf("Post %q: error parsing response JSON: %w", fullURL, err)
+	}
+
+	return sct, nil
+}
diff --git a/ctclient/log.go b/ctclient/log.go
index 93b2c88..d18d098 100644
--- a/ctclient/log.go
+++ b/ctclient/log.go
@@ -16,6 +16,12 @@ import (
 	"software.sslmate.com/src/certspotter/merkletree"
 )
 
+type WritableLog interface {
+	AddChain(context.Context, [][]byte) (*cttypes.SignedCertificateTimestamp, error)
+	AddPreChain(context.Context, [][]byte) (*cttypes.SignedCertificateTimestamp, error)
+	GetRoots(context.Context) ([][]byte, error)
+}
+
 type Log interface {
 	GetSTH(context.Context) (*cttypes.SignedTreeHead, string, error)
 	GetRoots(context.Context) ([][]byte, error)
diff --git a/ctclient/rfc6962.go b/ctclient/rfc6962.go
index 6ea4e74..0a7151b 100644
--- a/ctclient/rfc6962.go
+++ b/ctclient/rfc6962.go
@@ -31,6 +31,14 @@ type RFC6962LogEntry struct {
 	Extra_data []byte `json:"extra_data"`
 }
 
+func (ctlog *RFC6962Log) AddChain(ctx context.Context, chain [][]byte) (*cttypes.SignedCertificateTimestamp, error) {
+	return addChainOrPreChain(ctx, ctlog.HTTPClient, ctlog.URL, false, chain)
+}
+
+func (ctlog *RFC6962Log) AddPreChain(ctx context.Context, chain [][]byte) (*cttypes.SignedCertificateTimestamp, error) {
+	return addChainOrPreChain(ctx, ctlog.HTTPClient, ctlog.URL, true, chain)
+}
+
 func (ctlog *RFC6962Log) GetSTH(ctx context.Context) (*cttypes.SignedTreeHead, string, error) {
 	fullURL := ctlog.URL.JoinPath("/ct/v1/get-sth").String()
 	sth := new(cttypes.SignedTreeHead)
diff --git a/ctclient/static.go b/ctclient/static.go
index 9242a01..bf527a4 100644
--- a/ctclient/static.go
+++ b/ctclient/static.go
@@ -46,6 +46,14 @@ type StaticLogEntry struct {
 	chain            [][32]byte
 }
 
+func (ctlog *StaticLog) AddChain(ctx context.Context, chain [][]byte) (*cttypes.SignedCertificateTimestamp, error) {
+	return addChainOrPreChain(ctx, ctlog.HTTPClient, ctlog.SubmissionURL, false, chain)
+}
+
+func (ctlog *StaticLog) AddPreChain(ctx context.Context, chain [][]byte) (*cttypes.SignedCertificateTimestamp, error) {
+	return addChainOrPreChain(ctx, ctlog.HTTPClient, ctlog.SubmissionURL, true, chain)
+}
+
 func (ctlog *StaticLog) GetSTH(ctx context.Context) (*cttypes.SignedTreeHead, string, error) {
 	fullURL := ctlog.MonitoringURL.JoinPath("/checkpoint").String()
 	responseBody, err := get(ctx, ctlog.HTTPClient, fullURL)