The 5 Edge Cases That Broke Our Dev.to Auto-Crossposting (And How We Fixed Them)

In our previous post, we covered the producer-consumer problem for blog scheduling. But we glossed over the crossposting part.

"Just POST to the dev.to API," we said. "How hard could it be?"

Narrator: It was hard.

The Setup

We have a Node.js script that runs daily via GitHub Actions:

// Simplified flow
1. Find all markdown posts with publishAfter <= today
2. Check if they exist on dev.to already
3. If not, create them
4. Send Slack notification

Sounds straightforward. Here are the edge cases that broke it.

Edge Case 1: How Do You Know If a Post Already Exists?

The Problem

We can't just check our local database—we don't have one. The blog is a static site. So how do we avoid posting duplicates?

Naive approach: Keep a .crossposted.json file locally.

Why it fails: Someone manually posts to dev.to. Someone deletes the JSON file. Someone runs the script from a different machine. Duplicates everywhere.

The Fix: dev.to Is the Source of Truth

async fetchDevtoArticles() {
  const response = await fetch(`${DEVTO_API_URL}/me/published?per_page=100`, {
    headers: { 'api-key': this.apiKey },
  });

  const articles = await response.json();

  // Store by canonical_url for O(1) lookup
  for (const article of articles) {
    if (article.canonical_url) {
      this.devtoArticles.set(article.canonical_url, {
        id: article.id,
        url: article.url,
        title: article.title,
      });
    }
  }
}

Before creating anything, we fetch ALL our existing dev.to articles. The canonical_url field is unique—it's the original source URL. If our canonical URL already exists, skip.

Bonus: dev.to returns a 422 error with "canonical" in the message if you try to create a duplicate. We catch that too:

if (response.status === 422 && errorText.toLowerCase().includes('canonical')) {
  return { duplicate: true, title: frontmatter.title };
}

Belt and suspenders.

Edge Case 2: The 60-Day Time Bomb

The Problem

Our script only looks back 60 days on dev.to (performance optimization—we don't need articles from 2 years ago). But what happens to a post with publishAfter: "2025-01-01" that we never crossposted?

Scenario:

1. January: Write a post, set publishAfter: "2025-01-15"
2. January 15: Script runs, posts to dev.to ✅
3. March 20: 65 days later, the script's dev.to lookback window no longer includes this article
4. Some bug causes the post to be re-processed
5. Duplicate post on dev.to ❌

The Fix: Auto-Update Stale Dates

If a post has publishAfter older than 60 days, we automatically update it to today:

if (this.isOlderThanDevtoMaxDays(publishAfter)) {
  console.log(`[publish-after] "${title}" has old publishAfter (${publishAfter}), updating to ${today}`);
  return { shouldProcess: true, needsDateUpdate: true, newDate: today };
}

And here's the edge case's edge case—we need to commit this change to git:

// After processing all posts
if (this.filesToCommit.length > 0 && !this.dryRun) {
  commitChanges(this.filesToCommit, 'chore: auto-update old publishAfter dates to today');
}

function commitChanges(files, message) {
  for (const file of files) {
    execSync(`git add "${file}"`, { stdio: 'pipe' });
  }
  execSync(`git commit -m "${message}"`, { stdio: 'pipe' });
}

Why commit? Because if the script runs again before you pull, it would try to update the same posts again. The commit ensures the updated dates persist.

Slack notification: "⚠️ publishAfter updated to today for "My Post" - please pull latest"

Edge Case 3: Accidental Content Overwrites

The Problem

You crosspost a blog post. A week later, you fix a typo locally. The script runs. Does it update dev.to?

If yes: What if you intentionally made dev.to-specific edits? Gone.
If no: How do you push updates when you actually want them?

The Fix: Explicit Update Intent

Updates only happen when you set updatedAt in frontmatter:

---
title: "My Post"
publishAfter: "2026-02-15"
updatedAt: "2026-02-20"  # <-- This triggers the update
---

if (existingArticle) {
  if (frontmatter.updatedAt) {
    // Explicit intent to update - proceed
    result = await this.updateArticle(existingArticle.id, frontmatter, body);
  } else {
    // No updatedAt = skip (don't accidentally overwrite)
    console.log(`[exists] ${frontmatter.title}`);
    continue;
  }
}

No updatedAt? No update. Simple opt-in.

Edge Case 4: dev.to Rate Limiting

The Problem

dev.to allows 10 requests per 30 seconds. Try to crosspost 15 articles at once and you'll hit 429s.

The Fix: Delay + Retry with Backoff

// After each successful post
await new Promise(resolve => setTimeout(resolve, 3500)); // 3.5s delay

// On rate limit (429)
if (response.status === 429 && retryCount < CONFIG.maxRetries) {
  const retryAfter = parseInt(response.headers.get('retry-after'), 10) || 60;
  console.log(`[rate-limited] Waiting ${retryAfter}s before retry...`);
  await new Promise(r => setTimeout(r, retryAfter * 1000));
  return this.createArticle(frontmatter, body, retryCount + 1);
}

3.5 seconds between posts keeps us under the limit. If we do hit a 429, respect the retry-after header and try again.

Edge Case 5: Partial Failures

The Problem

You have 5 posts to crosspost. Posts 1 and 2 succeed. Post 3 fails (network error). What happens to posts 4 and 5?

The Fix: Continue on Failure + Report All

for (const file of files) {
  try {
    result = await this.createArticle(frontmatter, body);
    results.push({ action: 'created', title: frontmatter.title, url: result.url });
    await notifySlack(`Crossposted to dev.to: ${title} → ${result.url}`);
  } catch (error) {
    console.error(`[failed] ${frontmatter.title}: ${error.message}`);
    results.push({ action: 'failed', title: frontmatter.title, error: error.message });
    await notifySlack(`Failed to crosspost "${title}": ${error.message}`, true);
    // Continue to next post - don't abort
  }
}

// Exit with error code if any failures
if (failed > 0) {
  process.exit(1);
}

Every post gets attempted. Every result gets recorded. Every failure gets Slacked. The exit code tells CI whether to retry.

The Complete Slack Notification System

Here's every scenario that triggers a notification:

Slack Integration

One environment variable:

export SLACK_JO4_BLOGS_WH="https://hooks.slack.com/services/T00/B00/XXX"

That's it. The script handles the rest:

async function notifySlack(message, isWarning = false) {
  if (!CONFIG.slackWebhook) {
    console.log(`[slack-skip] ${message}`);
    return;
  }

  const emoji = isWarning ? '⚠️' : '✅';
  const text = `${emoji} *Jo4 Blog*: ${message}`;

  await fetch(CONFIG.slackWebhook, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ text }),
  });
}

No Slack webhook configured? It logs to console instead. Graceful degradation.

Configuration Knobs

const CONFIG = {
  localMaxDays: parseInt(process.env.LOCAL_MAX_DAYS, 10) || 30,
  devtoMaxDays: parseInt(process.env.DEVTO_MAX_DAYS, 10) || 60,
  maxRetries: 3,
  slackWebhook: process.env.SLACK_JO4_BLOGS_WH,
};

The Full Algorithm

1. Fetch all our articles from dev.to (last 60 days)
   → Store by canonical_url for O(1) lookup

2. For each local markdown file:
   a. Skip if draft or crosspost: false
   b. Skip if publishAfter > today (scheduled for future)
   c. If publishAfter is older than 60 days:
      → Update publishAfter to today
      → Queue file for git commit
      → Slack warning
   d. Check if canonical_url exists on dev.to:
      → If yes AND updatedAt is set: UPDATE
      → If yes AND no updatedAt: SKIP
      → If no: CREATE
   e. Wait 3.5 seconds (rate limiting)
   f. On 429: retry with backoff

3. Commit any auto-updated files to git

4. Report summary + exit code

Lessons Learned

1. Use the destination as source of truth - Don't maintain local state for external systems
2. Explicit > implicit - Updates require updatedAt flag, no accidental overwrites
3. Edge cases have edge cases - Old dates need auto-fixing, auto-fixes need git commits
4. Fail gracefully - Continue on error, report everything, use exit codes for CI
5. Integrate Slack early - One webhook URL, five notification scenarios, zero config UI

What edge cases have you hit with crossposting? Every automation has that one bug that only shows up at 3 AM.

Building jo4.io - URL shortener with analytics. Our blog auto-crossposts to dev.to using exactly this system.