diff --git a/src/processor.ts b/src/processor.ts
index eacf3c1..418ba0e 100644
--- a/src/processor.ts
+++ b/src/processor.ts
@@ -71,14 +71,24 @@ export async function processPullRequest(
     (config.overwriteTitle || weakTitle(pr.title, pr.headBranch));
   const updateBody =
     config.updateBody && (config.overwriteBody || emptyBody(pr.body));
-  if (!updateTitle && !updateBody && !config.comment) return;
+  console.info(
+    `PR #${pr.number} in ${pr.owner}/${pr.repo}: title=${updateTitle}, body=${updateBody}, comment=${config.comment}.`,
+  );
+  if (!updateTitle && !updateBody && !config.comment) {
+    console.info(`PR #${pr.number}: no fields are eligible; skipping.`);
+    return;
+  }
 
   const client = new GitHubClient({
     appId: config.appId,
     privateKey: config.privateKey,
     installationId: payload.installation.id,
   });
+  console.info(`PR #${pr.number}: collecting commits and changed files.`);
   const context = collectContext(await client.collectPullRequest(pr), config);
+  console.info(
+    `PR #${pr.number}: collected ${context.commits.length} commits and ${context.files.length} included files.`,
+  );
   let generated = fallbackNote(context);
   if (config.apiKey) {
     try {
@@ -91,10 +101,16 @@ export async function processPullRequest(
     }
   }
   const note = finalizeNote(generated, context);
-  if (updateTitle || updateBody)
+  if (updateTitle || updateBody) {
+    console.info(`PR #${pr.number}: updating pull request fields.`);
     await client.updatePullRequest(pr, {
       ...(updateTitle ? { title: note.title } : {}),
       ...(updateBody ? { body: mergeBody(note) } : {}),
     });
-  if (config.comment) await client.upsertComment(pr, renderComment(note));
+    console.info(`PR #${pr.number}: pull request fields updated.`);
+  }
+  if (config.comment) {
+    console.info(`PR #${pr.number}: writing managed comment.`);
+    await client.upsertComment(pr, renderComment(note));
+  }
 }
diff --git a/src/server.ts b/src/server.ts
index 9f0d798..e9de061 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -49,14 +49,25 @@ const server = createServer(async (request, response) => {
 
   const event = request.headers["x-github-event"];
   const delivery = request.headers["x-github-delivery"];
+  let payload: PullRequestOpenedPayload | undefined;
+  try {
+    payload = JSON.parse(body.toString("utf8")) as PullRequestOpenedPayload;
+  } catch (error) {
+    console.error(
+      `Webhook ${delivery ?? "unknown"} contains invalid JSON.`,
+      error,
+    );
+    response.writeHead(400).end("Invalid JSON");
+    return;
+  }
+  console.info(
+    `Received ${String(event)} webhook ${delivery ?? "unknown"} (action: ${payload.action ?? "none"}).`,
+  );
   response
     .writeHead(202, { "Content-Type": "application/json" })
     .end(JSON.stringify({ accepted: true, delivery }));
   if (event !== "pull_request") return;
   try {
-    const payload = JSON.parse(
-      body.toString("utf8"),
-    ) as PullRequestOpenedPayload;
     await processPullRequest(payload, config);
     console.info(`Processed webhook ${delivery ?? "unknown"}.`);
   } catch (error) {