Substack

Publish, edit, and manage Substack posts for the Alternative Partners publication (alternativepartners.substack.com) via the internal REST API. Use this skil...

Substack Skill

Manages publishing and editing for the Alternative Partners Substack publication via the internal REST API. No Playwright, no browser — pure requests with a session cookie.

Auth

This skill requires a connect.sid session cookie from Substack. Store it securely and provide it as the SUBSTACK_SID environment variable (or equivalent in your secrets manager).

This is the connect.sid cookie. Valid for months unless you sign out of Substack in Chrome. To rotate: sign out of Substack → sign back in → open DevTools → copy substack.sid cookie value → update your secrets store.

The publisher module at publishers/substack.py handles auth automatically. Always use it rather than calling the API directly.

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API Endpoints (alternativepartners.substack.com)

Action	Method	Endpoint
Create draft	POST	/api/v1/drafts
Publish draft	POST	/api/v1/drafts/{id}/publish
Update existing post	PUT	/api/v1/drafts/{id}
Fetch post by slug	GET	/api/v1/posts/{slug}
List posts	GET	/api/v1/posts?limit=N

Key discovery (2026-03-20): PUT /api/v1/drafts/{id} works on already-published posts too — it edits them in place. The post ID is the same as the draft ID used to create it.

Does NOT exist: PUT /api/v1/posts/{id} returns 404. Always use the /drafts/{id} endpoint even for published posts.

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Body Format

Substack uses ProseMirror JSON for post bodies. The publisher converts plain text → ProseMirror automatically.

Input format: Plain text with double-newline paragraph breaks. Output format (internal): ProseMirror doc object, serialized as a JSON string and passed as draft_body.

def _build_prosemirror_doc(body: str) -> dict:
    paragraphs = [p.strip() for p in body.strip().split("\n\n") if p.strip()]
    return {
        "type": "doc",
        "content": [
            {"type": "paragraph", "content": [{"type": "text", "text": p}]}
            for p in paragraphs
        ]
    }

Limitation: This produces plain paragraphs only. Bold, headers, lists, links require richer ProseMirror nodes — not yet implemented.

---

Common Operations

1. Publish a new post

from publishers.substack import publish_substack

url = publish_substack(
    title="Your Post Title",
    body="First paragraph.\n\nSecond paragraph.",
    publish=True   # False = save as draft only
)

Or via CLI from the pipeline directory:

cd ~/Documents/Codex/Content/ap-content-pipeline
python3 publishers/substack.py "Title Here" "Body paragraph one.\n\nParagraph two."

2. Update / edit an existing post

Need the numeric post ID. Get it by fetching the post:

curl -s -b "substack.sid=$SUBSTACK_SID" \
  "https://alternativepartners.substack.com/api/v1/posts/{slug}" \
  | python3 -c "import json,sys; d=json.load(sys.stdin); print('id:', d.get('id'))"

Then update:

from publishers.substack import update_substack

url = update_substack(
    post_id=191631753,
    title="Updated Title",
    body="New body content.\n\nSecond paragraph."
)

3. Get a post's ID from its slug

The slug is the last segment of the Substack URL: https://alternativepartners.substack.com/p/the-revops-ai-reality-check-nobodys → slug = the-revops-ai-reality-check-nobodys

curl -s -b "substack.sid=$SUBSTACK_SID" \
  "https://alternativepartners.substack.com/api/v1/posts/THE-SLUG-HERE" \
  | python3 -c "import json,sys; d=json.load(sys.stdin); print(d.get('id'))"

4. Save as draft without publishing

url = publish_substack(title, body, publish=False)
# Returns: https://alternativepartners.substack.com/publish/post/{id}

---

Email Blast Behavior

publish endpoint is called with {"send_email": False} — posts go live on the web but do not trigger a subscriber email blast. This is intentional for automated/pipeline posts.

To send an email blast, Benjamin needs to manually click "Send" in the Substack editor UI. Do not change send_email to True without explicit confirmation.

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Pipeline Integration

The AP Content Pipeline at ~/Documents/Codex/Content/ap-content-pipeline/ handles end-to-end publishing including veto window, soft-veto Slack notification, and scheduling. For single one-off posts, call the publisher directly. For managed pipeline runs, use publish_runner.py.

The pipeline also has a research_gate.py that runs a web search competitive sweep + LLM differentiation analysis before drafting. Posts in idea_inbox.json with research_status: "pending" will be researched before drafting. Requires a search API key configured in your environment.

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Troubleshooting

Symptom	Likely cause	Fix
401 Unauthorized	Cookie expired	Rotate: sign out/in of Substack in Chrome, grab new substack.sid, update your secrets store
PUT /api/v1/posts/... → 404	Wrong endpoint	Use /api/v1/drafts/{id} for updates, not /api/v1/posts/{id}
POST /api/v1/drafts/{id}/publish fails	Post already published	That's OK — post is already live, return the known URL
Body renders as one giant paragraph	Missing double-newlines	Input body must use \n\n between paragraphs
substack.sid not found	Cookie env var not set	Ensure SUBSTACK_SID is set in your environment before running