diff --git a/code/process-models/work-log/build.gradle b/code/process-models/work-log/build.gradle
new file mode 100644
index 00000000..507621c8
--- /dev/null
+++ b/code/process-models/work-log/build.gradle
@@ -0,0 +1,33 @@
+plugins {
+    id 'java'
+    id "io.freefair.lombok" version "8.2.2"
+
+    id 'jvm-test-suite'
+}
+
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(20))
+    }
+}
+dependencies {
+    implementation libs.lombok
+    annotationProcessor libs.lombok
+    implementation libs.bundles.slf4j
+
+    implementation libs.notnull
+
+    testImplementation libs.bundles.slf4j.test
+    testImplementation libs.bundles.junit
+    testImplementation libs.mockito
+}
+
+test {
+    useJUnitPlatform()
+}
+
+task fastTests(type: Test) {
+    useJUnitPlatform {
+        excludeTags "slow"
+    }
+}
diff --git a/code/process-models/work-log/src/main/java/nu/marginalia/worklog/BatchingWorkLog.java b/code/process-models/work-log/src/main/java/nu/marginalia/worklog/BatchingWorkLog.java
new file mode 100644
index 00000000..9c6ba9bb
--- /dev/null
+++ b/code/process-models/work-log/src/main/java/nu/marginalia/worklog/BatchingWorkLog.java
@@ -0,0 +1,35 @@
+package nu.marginalia.worklog;
+
+import java.io.IOException;
+
+/** The BatchingWorkLog is a work log for items of work performed in batches,
+ * where each batch needs to be finalized before the items it consists of can be
+ * considered done.  This is needed when the data is serialized into a format such
+ * as Parquet, where disparate items go into the same file, and the writer needs to be
+ * properly closed before the file can be read.
+ */
+public interface BatchingWorkLog extends AutoCloseable {
+
+    /** Returns true if logItem(id) has been run,
+     * and logFinishedBatch has been run after that.
+     */
+    boolean isItemCommitted(String id);
+
+    /** Returns true if logItem(id) has been run
+     * but not logFinishedBatch().
+     * <p/>
+     * Unlike isItemCommitted(), this state is ephemeral and not
+     * retained if e.g. the process crashes and resumes.
+     * */
+    boolean isItemInCurrentBatch(String id);
+
+    /** Log additional item to the current batch */
+    void logItem(String id) throws IOException;
+
+    /** Mark the current batch as finished and increment
+     * the batch number counter
+     */
+    void logFinishedBatch() throws IOException;
+
+    int getBatchNumber();
+}
diff --git a/code/process-models/work-log/src/main/java/nu/marginalia/worklog/BatchingWorkLogImpl.java b/code/process-models/work-log/src/main/java/nu/marginalia/worklog/BatchingWorkLogImpl.java
new file mode 100644
index 00000000..b1538b10
--- /dev/null
+++ b/code/process-models/work-log/src/main/java/nu/marginalia/worklog/BatchingWorkLogImpl.java
@@ -0,0 +1,221 @@
+package nu.marginalia.worklog;
+
+import java.io.*;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+import java.time.LocalDateTime;
+import java.util.HashSet;
+import java.util.Set;
+
+public class BatchingWorkLogImpl implements BatchingWorkLog {
+    private int batchNumber = 0;
+    private final Set<String> currentBatchItems = new HashSet<>(1000);
+    private final Set<String> commitedItems = new HashSet<>(10_000);
+    private final OutputStream writer;
+
+    public BatchingWorkLogImpl(Path file) throws IOException  {
+        if (Files.exists(file)) {
+            try (var linesStream = Files.lines(file)) {
+                linesStream.map(WorkLogItem::parse).forEach(
+                        item -> item.replay(this)
+                );
+            }
+
+            writer = Files.newOutputStream(file, StandardOpenOption.APPEND);
+            writeLogEntry(new CommentLine("Log resumed on " + LocalDateTime.now()));
+            if (getCurrentBatchSize() > 0) {
+                writeLogEntry(new CrashMarker());
+            }
+        }
+        else {
+            writer = Files.newOutputStream(file, StandardOpenOption.CREATE_NEW);
+            writeLogEntry(new CommentLine("Log created on " + LocalDateTime.now()));
+            writeLogEntry(new CommentLine(" Format: "));
+            writeLogEntry(new CommentLine(" " + AddItem.MARKER + " ID\tsignifies adding an item to the current batch"));
+            writeLogEntry(new CommentLine(" " + FinishBatch.MARKER + "\tsignifies finalizing the current batch and switching to the next"));
+            writeLogEntry(new CommentLine(" " + CrashMarker.MARKER + "\tdiscard contents from the current batch and start over, written after a crash"));
+            writeLogEntry(new CommentLine("Upon a crash, items that have re-process until their batch is finalized"));
+        }
+
+
+    }
+
+    void writeLogEntry(WorkLogItem item) throws IOException {
+        item.write(this);
+    }
+
+    void writeLine(String line) throws IOException {
+        writer.write(line.getBytes(StandardCharsets.UTF_8));
+        writer.write('\n');
+        writer.flush();
+    }
+
+    @Override
+    public boolean isItemCommitted(String id) {
+        return commitedItems.contains(id);
+    }
+
+    @Override
+    public boolean isItemInCurrentBatch(String id) {
+        return currentBatchItems.contains(id);
+    }
+    @Override
+    public void logItem(String id) throws IOException {
+        writeLogEntry(new AddItem(id));
+    }
+
+    @Override
+    public void logFinishedBatch() throws IOException {
+        writeLogEntry(new FinishBatch());
+        incrementBatch();
+    }
+
+    void incrementBatch() {
+        batchNumber++;
+
+        // Transfer all items from the current batch to the committed items' batch
+        commitedItems.addAll(currentBatchItems);
+        currentBatchItems.clear();
+    }
+
+    void restartBatch() {
+        currentBatchItems.clear();
+    }
+
+    void addItemToCurrentBatch(String id) {
+        currentBatchItems.add(id);
+    }
+
+    @Override
+    public void close() throws IOException {
+        writer.flush();
+        writer.close();
+    }
+
+    @Override
+    public int getBatchNumber() {
+        return batchNumber;
+    }
+
+    public int getCurrentBatchSize() {
+        return currentBatchItems.size();
+    }
+}
+
+interface WorkLogItem {
+
+    void replay(BatchingWorkLogImpl bwl);
+    void write(BatchingWorkLogImpl bwl) throws IOException;
+
+    static WorkLogItem parse(String line) {
+        if (line.isBlank())
+            return new BlankLine();
+
+        var lineParts = LogLineParts.parse(line);
+
+        return switch (lineParts.tag()) {
+            case CommentLine.MARKER -> new CommentLine(lineParts.arg());
+            case AddItem.MARKER -> new AddItem(lineParts.arg());
+            case FinishBatch.MARKER -> new FinishBatch();
+            case CrashMarker.MARKER -> new CrashMarker();
+            default -> throw new WorkLogParseException(line);
+        };
+    }
+}
+
+record LogLineParts(char tag, String arg) {
+    public static LogLineParts parse(String line) {
+        line = line.trim();
+
+        char tag = line.charAt(0);
+        String arg = line.substring(1).trim();
+
+        int commentIdx = arg.indexOf('#');
+        if (commentIdx >= 0) arg = arg.substring(0, commentIdx).trim();
+
+        return new LogLineParts(tag, arg);
+    }
+}
+
+record CommentLine(String comment) implements WorkLogItem {
+    final static char MARKER = '#';
+
+    @Override
+    public void replay(BatchingWorkLogImpl bwl) {}
+
+    @Override
+    public void write(BatchingWorkLogImpl bwl) throws IOException {
+        bwl.writeLine(MARKER + " " + comment);
+    }
+}
+record BlankLine() implements WorkLogItem {
+    final static char MARKER = ' ';
+
+    @Override
+    public void replay(BatchingWorkLogImpl bwl) {}
+
+    @Override
+    public void write(BatchingWorkLogImpl bwl) throws IOException {
+        bwl.writeLine(MARKER + "");
+    }
+}
+
+record FinishBatch() implements WorkLogItem {
+    final static char MARKER = 'F';
+
+    @Override
+    public void replay(BatchingWorkLogImpl bwl) {
+        bwl.incrementBatch();
+    }
+
+    @Override
+    public void write(BatchingWorkLogImpl bwl) throws IOException {
+        bwl.writeLine("# " + LocalDateTime.now());
+        bwl.writeLine("# finalizing batchNumber = " + bwl.getBatchNumber());
+        bwl.writeLine(Character.toString(MARKER));
+    }
+
+
+}
+
+record CrashMarker() implements WorkLogItem {
+    final static char MARKER = 'X';
+
+    @Override
+    public void replay(BatchingWorkLogImpl bwl) {
+        bwl.restartBatch();
+    }
+
+    @Override
+    public void write(BatchingWorkLogImpl bwl) throws IOException {
+        bwl.writeLine("# " + LocalDateTime.now());
+        bwl.writeLine("# discarding batchNumber = " + bwl.getBatchNumber());
+        bwl.writeLine(Character.toString(MARKER));
+    }
+
+
+}
+record AddItem(String id) implements WorkLogItem {
+    final static char MARKER = '+';
+
+    @Override
+    public void replay(BatchingWorkLogImpl bwl) {
+        bwl.addItemToCurrentBatch(id);
+    }
+
+    @Override
+    public void write(BatchingWorkLogImpl bwl) throws IOException {
+        bwl.writeLine(MARKER + " " + id);
+    }
+}
+
+class WorkLogParseException extends RuntimeException {
+    @Serial
+    private static final long serialVersionUID = -1238138989389021166L;
+
+    public WorkLogParseException(String logLine) {
+        super("Failed to parse work log line: '" + logLine + "'");
+    }
+}
\ No newline at end of file
diff --git a/code/process-models/work-log/src/test/java/nu/marginalia/worklog/BatchingWorkLogImplTest.java b/code/process-models/work-log/src/test/java/nu/marginalia/worklog/BatchingWorkLogImplTest.java
new file mode 100644
index 00000000..fa765fd2
--- /dev/null
+++ b/code/process-models/work-log/src/test/java/nu/marginalia/worklog/BatchingWorkLogImplTest.java
@@ -0,0 +1,63 @@
+package nu.marginalia.worklog;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class BatchingWorkLogImplTest {
+    Path fileName;
+
+    @BeforeEach
+    public void setUp() throws IOException {
+        fileName = Files.createTempFile(getClass().getSimpleName(), ".test");
+    }
+
+    @AfterEach
+    public void tearDown() throws IOException {
+        Files.deleteIfExists(fileName);
+    }
+
+    @Test
+    public void testResumeOnEmptyFile() throws IOException {
+        Files.delete(fileName);
+
+        try (var wl = new BatchingWorkLogImpl(fileName)) {
+            wl.logItem("1");
+            wl.logItem("2");
+            wl.logItem("3");
+            wl.logFinishedBatch();
+            wl.logItem("4");
+            wl.logItem("5");
+            wl.logFinishedBatch();
+            wl.logItem("6");
+        }
+
+        try (var wl = new BatchingWorkLogImpl(fileName)) {
+            assertTrue(wl.isItemCommitted("1"));
+            assertTrue(wl.isItemCommitted("2"));
+            assertTrue(wl.isItemCommitted("3"));
+            assertTrue(wl.isItemCommitted("4"));
+            assertTrue(wl.isItemCommitted("5"));
+            assertFalse(wl.isItemCommitted("6"));
+            wl.logItem("7");
+            wl.logFinishedBatch();
+        }
+        try (var wl = new BatchingWorkLogImpl(fileName)) {
+            assertTrue(wl.isItemCommitted("1"));
+            assertTrue(wl.isItemCommitted("2"));
+            assertTrue(wl.isItemCommitted("3"));
+            assertTrue(wl.isItemCommitted("4"));
+            assertTrue(wl.isItemCommitted("5"));
+            assertFalse(wl.isItemCommitted("6"));
+            assertTrue(wl.isItemCommitted("7"));
+        }
+
+        Files.readAllLines(fileName).forEach(System.out::println);
+    }
+}
\ No newline at end of file
diff --git a/settings.gradle b/settings.gradle
index 884160c9..d2b54d41 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -65,6 +65,7 @@ include 'code:processes:test-data'
 
 include 'code:process-models:converting-model'
 include 'code:process-models:crawling-model'
+include 'code:process-models:work-log'
 
 include 'code:tools:term-frequency-extractor'
 include 'code:tools:crawl-job-extractor'