diff --git a/client/mirror/README.md b/client/mirror/README.md
new file mode 100644
index 000000000..ba91b079c
--- /dev/null
+++ b/client/mirror/README.md
@@ -0,0 +1,7 @@
+# tlog-mirror client
+
+This directory contains an experimental/WIP client implementation of the
+[tlog-mirror](https://c2sp.org/tlog-mirror) spec.
+
+Everything under this directory may be subject to large and unannounced changes
+and so should be considered excluded from the SemVer policy for the time being.
diff --git a/client/mirror/client.go b/client/mirror/client.go
new file mode 100644
index 000000000..29e832ae7
--- /dev/null
+++ b/client/mirror/client.go
@@ -0,0 +1,256 @@
+// Copyright 2026 The Tessera authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package mirror provides client support for pushing checkpoints and entries
+// to a mirror server compliant with the [tlog-mirror spec].
+//
+// [tlog-mirror spec]: https://c2sp.org/tlog-mirror
+package mirror
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+
+	"github.com/transparency-dev/tessera/client"
+)
+
+// PackageProver is an interface for generating proof hashes required for
+// the entry package covering the index interval [start, end).
+type PackageProver interface {
+	// PackageProof computes and returns the proof hashes required by
+	// the mirror for the specified entry package.
+	PackageProof(ctx context.Context, start, end uint64) ([][]byte, error)
+}
+
+// Options holds the configuration for a tlog-mirror Client.
+type Options struct {
+	mirrorURL               *url.URL
+	httpClient              *http.Client
+	logOrigin               string
+	tileFetcher             client.TileFetcherFunc
+	bundleFetcher           client.EntryBundleFetcherFunc
+	mirrorCheckpointFetcher client.CheckpointFetcherFunc
+	prover                  PackageProver
+}
+
+// NewOptions returns a new Options object with default values.
+func NewOptions() *Options {
+	return &Options{
+		httpClient: http.DefaultClient,
+	}
+}
+
+// WithMirrorURL sets the mirror URL.
+func (o *Options) WithMirrorURL(mirrorURL *url.URL) *Options {
+	o.mirrorURL = mirrorURL
+	return o
+}
+
+// WithHTTPClient sets the HTTP client.
+func (o *Options) WithHTTPClient(httpClient *http.Client) *Options {
+	o.httpClient = httpClient
+	return o
+}
+
+// WithLogOrigin sets the log origin.
+func (o *Options) WithLogOrigin(logOrigin string) *Options {
+	o.logOrigin = logOrigin
+	return o
+}
+
+// WithTileFetcher sets the tile fetcher.
+func (o *Options) WithTileFetcher(tileFetcher client.TileFetcherFunc) *Options {
+	o.tileFetcher = tileFetcher
+	return o
+}
+
+// WithBundleFetcher sets the entry bundle fetcher.
+func (o *Options) WithBundleFetcher(bundleFetcher client.EntryBundleFetcherFunc) *Options {
+	o.bundleFetcher = bundleFetcher
+	return o
+}
+
+// WithMirrorCheckpointFetcher sets the mirror checkpoint fetcher.
+func (o *Options) WithMirrorCheckpointFetcher(mirrorCheckpointFetcher client.CheckpointFetcherFunc) *Options {
+	o.mirrorCheckpointFetcher = mirrorCheckpointFetcher
+	return o
+}
+
+// WithProver sets the package prover.
+func (o *Options) WithProver(prover PackageProver) *Options {
+	o.prover = prover
+	return o
+}
+
+// validate checks that the Options are valid.
+func (o *Options) validate() error {
+	if o.mirrorURL == nil {
+		return errors.New("mirror URL is required")
+	}
+	if o.httpClient == nil {
+		return errors.New("HTTP client is required")
+	}
+	if o.logOrigin == "" {
+		return errors.New("log origin is required")
+	}
+	if o.tileFetcher == nil {
+		return errors.New("tile fetcher is required")
+	}
+	if o.bundleFetcher == nil {
+		return errors.New("bundle fetcher is required")
+	}
+	if o.mirrorCheckpointFetcher == nil {
+		return errors.New("mirror checkpoint fetcher is required")
+	}
+	if o.prover == nil {
+		return errors.New("prover is required")
+	}
+	return nil
+}
+
+// Client is a push-based client designed to synchronize entries and checkpoints
+// from a source log to a tlog-mirror compliant server.
+// TODO(roger2hk): Should multiple mirrors in one client be supported?
+type Client struct {
+	opts *Options
+}
+
+// NewClient creates a new Client with the provided options.
+func NewClient(_ context.Context, opts Options) (*Client, error) {
+	if err := opts.validate(); err != nil {
+		return nil, err
+	}
+
+	return &Client{opts: &opts}, nil
+}
+
+// ErrConflict is returned by tlog-mirror client operations when the mirror returns a 409 Conflict.
+type ErrConflict struct {
+	PendingSize uint64
+	NextEntry   uint64
+	Ticket      []byte
+}
+
+func (e ErrConflict) Error() string {
+	return fmt.Sprintf("mirror sync conflict: pending size %d, next entry %d, ticket length %d", e.PendingSize, e.NextEntry, len(e.Ticket))
+}
+
+// parseConflict parses the text/x.tlog.mirror-info body of a 409 Conflict response.
+// Format:
+//   - The tree size of a valid pending checkpoint, in decimal
+//   - The next entry, in decimal
+//   - An opaque, possibly zero length, ticket value, encoded in base64
+//
+// nolint:unused
+func parseConflict(r io.Reader) (ErrConflict, error) {
+	// TODO(roger2hk): Implement this.
+
+	return ErrConflict{}, errors.New("TODO")
+}
+
+// pushEntries streams entry packages and their proofs to the mirror's /add-entries endpoint.
+// nolint:unused
+func (c *Client) pushEntries(ctx context.Context, uploadStart, uploadEnd uint64, ticket []byte) error {
+	pr, _ := io.Pipe()
+
+	// TODO(roger2hk): Implement streaming entries.
+
+	u, err := c.opts.mirrorURL.Parse("add-entries")
+	if err != nil {
+		return fmt.Errorf("failed to parse add-entries URL: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, u.String(), pr)
+	if err != nil {
+		return fmt.Errorf("failed to create HTTP request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/octet-stream")
+	req.Header.Set("Content-Encoding", "gzip")
+
+	resp, err := c.opts.httpClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("POST %s failed: %w", u, err)
+	}
+	defer func() {
+		_ = resp.Body.Close()
+	}()
+
+	if resp.StatusCode == http.StatusConflict {
+		conflict, err := parseConflict(resp.Body)
+		if err != nil {
+			return fmt.Errorf("conflict returned, but failed to parse response body: %w", err)
+		}
+		return conflict
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return fmt.Errorf("add-entries failed with status %d: %s", resp.StatusCode, string(body))
+	}
+
+	return nil
+}
+
+// pushCheckpoint sends a new checkpoint and its consistency proof to the mirror's /add-checkpoint endpoint.
+// nolint:unused
+func (c *Client) pushCheckpoint(ctx context.Context, oldSize uint64, proof [][]byte, checkpointRaw []byte) ([]byte, error) {
+	// TODO(roger2hk): Implement checkpoint.
+	var reqBody io.Reader
+
+	u, err := c.opts.mirrorURL.Parse("add-checkpoint")
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse add-checkpoint URL: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, u.String(), reqBody)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create HTTP request: %w", err)
+	}
+	req.Header.Set("Content-Type", "text/plain") // add-checkpoint uses standard line-oriented payload
+
+	resp, err := c.opts.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("POST %s failed: %w", u, err)
+	}
+	defer func() {
+		_ = resp.Body.Close()
+	}()
+
+	if resp.StatusCode != http.StatusOK {
+		respBody, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("add-checkpoint failed with status %d: %s", resp.StatusCode, string(respBody))
+	}
+
+	cosigs, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read cosignatures from response body: %w", err)
+	}
+
+	return cosigs, nil
+}
+
+// Sync synchronizes all entries and the checkpoint from the source log to the mirror
+// up to the specified targetSize. It returns the mirror's cosignatures on success.
+func (c *Client) Sync(ctx context.Context, targetCheckpointRaw []byte, targetSize uint64) ([]byte, error) {
+	// TODO(roger2hk):
+	// 1. Get the mirror's current state by querying it with upload_start=0, upload_end=0 (guaranteed to conflict).
+	// 2. If the mirror's pending checkpoint is smaller than target size, update it first.
+	// 3. Push entries up to target size in packages of 256, handling concurrent conflicts and retries.
+
+	return nil, errors.New("WIP")
+}