substack-mcp

The demo runs actual MCP handlers against offline sample data. No live API calls or publication occur. Follow the draft workflow to create, find, export and review a post.

Safe by design — with one loud exception: This server cannot publish or delete long-form posts. Post tools create and edit drafts only; you review and publish manually through Substack's editor. The exception is Substack Notes: create_note and create_note_with_link publish short-form Notes immediately, because Notes have no draft state on Substack. Treat the Note tools as public-publish actions — there is no preview step and no undo from this server. The split is proportionate review, the piece of trust infrastructure for agents this server cares most about: the high-stakes surface gets a human gate, and the exception is stated loudly.

This server imposes no Bestseller-status check. Use an authenticated account with permission to manage the publication; individual operations depend on your Substack access. Connect through local stdio or self-hosted HTTP.

For 1.0 setup coverage and account eligibility, see compatibility. Maintainers can use the release checklist and distribution inventory.

Contents: Quick start · Setup · Tools · Operator CLI · Draft workflow · Export · Markdown · Multiple publications · Transports · Compatibility

1. Install and sign in. Browser login needs the optional Playwright dependency:

   npm install @conorbronsdon/substack-mcp playwright
   npx playwright install chromium
   npx substack-mcp login https://yourblog.substack.com --user-id 12345

   Use your own account's user ID. The session is saved only after a bounded authenticated read succeeds. To paste credentials instead, see Option B.

2. Verify a read. npx substack-mcp doctor --json --check-auth makes one bounded read per publication. It confirms read access, not your user ID or write permission.

3. Connect your MCP client. Add the server to Claude Desktop or Claude Code, or use the Codex plugin. Environment variables take precedence; omit them to use the stored browser-login session. Then ask your assistant: "How many Substack subscribers do I have?"

4. Prepare a draft for review. Follow the draft workflow: create_draft, search_posts, export_draft, preflight_draft, then plan_draft_update and update_draft. Long-form posts stay unpublished drafts until you publish them in Substack's editor. create_note and create_note_with_link publish immediately.

Requires Node.js 22 or newer (CI covers Node 22 and 24). Browser login additionally requires Playwright.

You can supply credentials two ways: paste them as env vars (below), or run the optional browser login which captures and stores them for you.

Install the server and optional Playwright dependency together in a local tools directory, then sign in:

npm install @conorbronsdon/substack-mcp playwright
npx playwright install chromium
npx substack-mcp login https://yourblog.substack.com --user-id 12345

substack-mcp-login remains a supported alias. Missing publication URL and user ID are prompted. Supply your own account's user ID; a post author's byline does not verify your identity. The browser opens for sign-in, including any CAPTCHA. Only a cookie applicable to the publication API is captured, and a bounded authenticated read must succeed before saving. This verifies read access, not the configured user ID or permission to write.

Without --profile, login saves ~/.substack-mcp/session.json (directory override: SUBSTACK_MCP_HOME). The server uses this legacy session when publication credential environment variables and SUBSTACK_PROFILES are unset.

Storage: sessions use AES-256-GCM with a key derived from the OS account and machine. File permissions request 0600; Windows access also depends on directory ACLs. This is a machine-bound file, not an OS keychain or secret vault. Code running as your OS user can derive the key. Use environment credentials if your MCP client manages secrets for you.

npx substack-mcp login https://yourblog.substack.com --user-id 12345 --profile work
npx substack-mcp profiles list
# Copy an existing legacy session without changing its file:
npx substack-mcp profiles migrate --name personal

Keys start with a lowercase ASCII letter and contain only lowercase letters, digits and hyphens, up to 64 characters. Existing profiles require explicit --force to replace. List output contains keys, readability status, publication origins and file save times; it excludes cookies and user IDs. Unreadable profiles remain visible but cannot be selected. Save time records local persistence, including migration; it is not token issuance or expiration time. Listing is bounded to 32 profiles.

Profile storage requires a local filesystem supporting hard links (such as NTFS or a typical Linux filesystem), so creation can install a complete encrypted file without overwriting an existing name. FAT/exFAT and some network mounts are not supported: set SUBSTACK_MCP_HOME to a suitable local directory. Do not use --force to work around an unsupported filesystem.

Set SUBSTACK_PROFILES=work,personal in your MCP client's environment to select up to 32 distinct profiles. Remove all publication credential variables first: combining profile selection with legacy or named credential variables is an error, including empty variables. Missing, corrupt or invalid selected profiles stop startup; they never fall back to another account. Profiles on disk are never activated by discovery. With multiple profiles, tools require an explicit publication key and CLI reads require --publication.

To roll back, unset SUBSTACK_PROFILES and restore your previous environment configuration. Migration preserves the legacy session byte-for-byte. These files use the existing encryption format; an OS keychain is not currently supported. Run substack-mcp status --json for offline configuration diagnostics or substack-mcp doctor --check-auth --json for a bounded read per selected account.

Open your Substack in a browser, then:

1. Session token: Navigate to your publication, open DevTools → Application → Cookies → copy the value of connect.sid (URL-encoded string starting with s%3A)
2. User ID: Use the numeric ID of your signed-in Substack account from your authenticated account data. Do not use a publication post's byline ID: publications can have multiple authors. This server does not independently verify the supplied ID.
3. Publication URL: Your Substack URL, including custom domain if you have one (e.g., https://newsletter.yourdomain.com or https://yourblog.substack.com)

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "substack": {
      "command": "npx",
      "args": ["-y", "@conorbronsdon/substack-mcp"],
      "env": {
        "SUBSTACK_PUBLICATION_URL": "https://yourblog.substack.com",
        "SUBSTACK_SESSION_TOKEN": "your-session-token",
        "SUBSTACK_USER_ID": "your-user-id"
      }
    }
  }
}

Claude Code and Codex plugin setup is available alongside manual MCP configuration. The repository marketplace and local plugin are separate from curated-directory acceptance or hosted ChatGPT support.

Add to your .mcp.json:

{
  "mcpServers": {
    "substack": {
      "command": "npx",
      "args": ["-y", "@conorbronsdon/substack-mcp"],
      "env": {
        "SUBSTACK_PUBLICATION_URL": "https://yourblog.substack.com",
        "SUBSTACK_SESSION_TOKEN": "your-session-token",
        "SUBSTACK_USER_ID": "your-user-id"
      }
    }
  }
}

Ask your AI assistant: "How many Substack subscribers do I have?"

Tool output compatibility, response limits and versioning are documented in the tool contract.

The CLI exposes operator commands and configuration checks through the same MCP handlers and credential resolution as the server. drafts create writes one private draft; the other operator commands read:

substack-mcp status --json
substack-mcp doctor --json --check-auth
substack-mcp drafts list --limit 10

Commands, the JSON envelope, exit codes, request deadlines and response limits are documented in operator CLI and diagnostics.

Every tool declares explicit MCP side-effect annotations; see tool annotations. Tool descriptions carry the authoritative wording.

search_posts accepts query (1–500 characters), status (published, drafts, or scheduled, default published), offset (default 0), and limit (1–50, default 25). It makes one authenticated archive request and returns projected metadata, returned, total, has_more, and next_offset. Continue with next_offset and the same query/status. When Substack omits the total and a page is full, has_more is null (unknown); another page may be empty. Substack controls matching and indexing: this is not a guaranteed full-text scan. Use get_post or get_draft to retrieve full content. Pagination is not a snapshot; concurrent edits can move results between pages.

preflight_draft accepts draft_id, reads it once, and returns checks_passed, findings with severity/code/message, content counts and an editor link. It checks title, audience, JSON/body shape, image wrappers and HTTPS sources, and paywall count and edge placement. Unknown nodes and external images produce review warnings. Bodies over two million characters, 10,000 nodes, or depth 100 are not fully checked; counts.complete is false and aggregate checks are skipped after a scan limit. Unknown-node warnings name up to five types for editor review. This is a focused static check, not full ProseMirror validation or publish approval. It does not fetch links/images, verify access settings, or prove final rendering. Review the draft in Substack; no content is modified.

Both tools require publication when multiple publications are configured.

In 0.9, call plan_draft_update, review its output, then call update_draft with the same fields and returned receipt. Published or known stale drafts are rejected. The read/write race remains; check readback outcomes and review in Substack. The CLI shares this flow through drafts plan and drafts apply. See draft changes and migration for examples and limits.

Notes have no draft state on Substack, so there is no draft-first option for these two tools.

add_free_subscriber adds one consenting reader to the free newsletter. It is a distribution change: that reader may receive future newsletter emails. It can request a welcome email with send_welcome_email: true (off by default). It never grants paid access or overrides Substack's suppression of previously unsubscribed addresses. Its MCP annotations identify it as an external write (readOnlyHint: false, openWorldHint: true).

{"email":"reader@example.org","consent_confirmed":true,"consent_evidence":{"source":"booking:message-id","recorded_at":"2026-09-01T00:00:00Z"},"dry_run":true}

Dry-run is the default. After checking actual newsletter consent, set dry_run: false to execute. Live adds require the source reference and timestamp in consent_evidence; this attestation is echoed with the publication key for auditing and does not replace checking the underlying consent record. Multi-publication configurations also require the publication selector, just like every other tool.

Results distinguish existing, dry_run, verified, blocked, and unverified, busy, and retryable. busy performs no write; wait for the other operation. retryable means authentication or rate limiting refused the request; resolve that condition before explicitly retrying. An empty API acknowledgement is not proof of addition. verified means an exact membership lookup succeeded after the request; it does not prove that this request originally created the membership. Dashboard data can lag. A missing reader may also have previously unsubscribed.

For unverified, recheck with get_subscriber; never automatically repeat the add. For blocked, review in Substack without bypassing suppression. Automated callers must persist an attempt ledger before sending each live request. The client's in-memory duplicate guard does not survive restarts or separate HTTP sessions. Keep subscriber identities and consent evidence out of shared repositories, prompts to unapproved public services, and routine logs.

Implementation and live verification notes: subscriber API.

For Google Calendar booking opt-ins, the calendar sync helper provides a bounded Gmail scan, latest-answer selection, a private durable attempt ledger, and read-only reconciliation after uncertain writes. Scheduling is an explicit local setup step; installing the MCP does not start a background job.

• Publish posts — Publishing long-form posts should be a deliberate human action (Notes are the documented exception above)
• Delete — Too destructive for an AI tool
• Schedule — Use Substack's editor for scheduling. (list_scheduled_posts reads what you've queued there, but this server never creates, edits, or cancels a schedule.)

For an always-on scheduler with durable cloud state and weekly email reports, see Cloud Calendar sync.

Running more than one publication behind a single server? Set a SUBSTACK_PUB_<KEY>_* triplet per publication instead of the plain SUBSTACK_* vars. <KEY> is any name you choose (letters, digits, underscores) — it becomes the publication's lowercase, hyphenated key, e.g. KEVIN_MULDOON → kevin-muldoon.

"env": {
  "SUBSTACK_PUB_KEVIN_MULDOON_PUBLICATION_URL": "https://kevinmuldoon.substack.com",
  "SUBSTACK_PUB_KEVIN_MULDOON_SESSION_TOKEN": "token-1",
  "SUBSTACK_PUB_KEVIN_MULDOON_USER_ID": "111",
  "SUBSTACK_PUB_SAPERE_PUBLICATION_URL": "https://sapere.substack.com",
  "SUBSTACK_PUB_SAPERE_SESSION_TOKEN": "token-2",
  "SUBSTACK_PUB_SAPERE_USER_ID": "222"
}

Each triplet is independent, and setting any SUBSTACK_PUB_<KEY>_* variable declares that publication. An incomplete triplet — a missing variable, an empty value, or a whitespace-only value — fails startup with an error naming the key, rather than silently dropping that publication. That matters because a dropped publication is not "one fewer publication": drop the only one and the server falls back to your stored browser-login session; drop one of two and every tool loses its publication parameter, so a call meant for the dropped publication routes silently to the surviving one.

Keys are compared case-insensitively, with _ folded to -. Two names that resolve to the same key (SUBSTACK_PUB_ALPHA_* and SUBSTACK_PUB_Alpha_*) are a startup error too — merging them silently would let one publication's URL pair with another's session token.

<KEY> accepts ASCII letters, digits, and underscores; the three suffixes must be uppercase and the whole name must have no stray whitespace. Anything that begins with SUBSTACK_PUB_ but does not fit that shape — a hyphen in the key, a lowercase suffix, an accented character, a trailing space — is a startup error naming the variable, not a variable that gets quietly ignored. For the same reason as above: an ignored publication is not one fewer publication, it is a silent reroute to a different one.

With two or more publications configured, every tool gains a required publication parameter — one of your configured keys (e.g. kevin-muldoon, sapere above). The calling model must specify one on every call; an unrecognized value is rejected before any Substack API call is made, so a stray write can't land on the wrong publication. With exactly one publication configured — the common case, whether via plain SUBSTACK_* vars or a single SUBSTACK_PUB_<KEY>_* triplet — no publication parameter is added at all; every tool's schema is unchanged from single-publication mode.

Don't mix the two styles: if any SUBSTACK_PUB_<KEY>_* var is set, the plain SUBSTACK_* vars are ignored (with a startup warning) rather than treated as an unnamed extra publication.

SUBSTACK_USER_AGENT and SUBSTACK_REQUEST_TIMEOUT_MS apply to every configured publication — they are not per-publication. Browser login also supports explicit named profiles; see Named profiles and migration.

Substack session tokens expire periodically (typically ~90 days). If you get authentication errors, grab a fresh connect.sid cookie from your browser and update the env var (make sure ad blockers are disabled when copying the cookie) — or, if you used the browser login, just re-run substack-mcp-login to refresh the stored session.

Substack publications served on a custom domain (e.g. blog.example.com) sit behind Cloudflare, which can reject non-browser requests with 403 error code: 1010. To avoid this, the server sends a browser User-Agent and a Referer by default, and addresses the publication by its canonical *.substack.com host.

• Use the canonical host. Set SUBSTACK_PUBLICATION_URL to the publication's *.substack.com address rather than the custom domain. Calls to the canonical host are served directly; custom-domain calls may 301-redirect and then 401.
• Override the User-Agent (optional) via SUBSTACK_USER_AGENT if you need a different browser signature:

"env": {
  "SUBSTACK_PUBLICATION_URL": "https://yourblog.substack.com",
  "SUBSTACK_SESSION_TOKEN": "your-session-token",
  "SUBSTACK_USER_ID": "your-user-id",
  "SUBSTACK_USER_AGENT": "Mozilla/5.0 ..."
}

Every request to Substack is bounded by a 30-second deadline. Node applies no request timeout of its own — only a 10-second connect timeout — so a host that accepts the connection and then goes silent (a proxy that drops packets rather than refusing them) would otherwise hang a tool call indefinitely. A request that hits the deadline fails with a TimeoutError naming the endpoint and the limit.

Raise or lower it with SUBSTACK_REQUEST_TIMEOUT_MS (milliseconds; a non-numeric or non-positive value is ignored with a warning and the default is used):

"env": {
  "SUBSTACK_REQUEST_TIMEOUT_MS": "60000"
}

By default the server speaks MCP over stdio, which the client configurations above assume. Set MCP_TRANSPORT=http for a stateless Streamable HTTP server (POST /mcp, GET /health) in a persistent, self-hosted deployment. Setup, listener variables and the security model are in HTTP transport.

The HTTP listener starts closed: loopback Host and Origin allowlists by default, an optional bearer token (MCP_HTTP_TOKEN) and a 10 MiB body cap. Host and Origin checks are not authentication; set a token wherever other processes can reach the port. See the listener policy.

Versioned GHCR images and transport verification: container distribution.

API failures map to typed errors (AuthenticationError, RateLimitError, ValidationError, NotFoundError, ServerError, TimeoutError, and the base SubstackAPIError). The status mapping and error-body parsing are documented in typed errors.

Use export_draft for a read-only Markdown/JSON bundle, or run:

substack-mcp export 42 --output draft-export.json
substack-mcp export 42 --format markdown --output draft.md

Markdown exports retain the exact original body in a .source.json sidecar. Inspect unsupported_nodes before reuse. Existing files require --force. See export and CLI behavior for publication selection, limits, partial exports and file recovery.

Drafts accept CommonMark/GFM Markdown: headings, nested bold/italic/strikethrough, links and reference links, images with captions and linked destinations, nested lists with starting numbers, code, blockquotes, rules and hard breaks. A standalone <!-- paywall --> block adds one paywall to a long-form draft.

Unsupported content returns unsupported_nodes before a write. After reviewing those diagnostics, draft callers can explicitly set allow_unsupported: true to retain literal fallbacks. Tables remain Markdown inside code blocks; native tables, callouts and arbitrary embeds are not advertised as supported. Footnotes in top-level paragraphs map to the editor's native footnotes in long-form drafts. Notes reject unsupported conversion before either publication or attachment creation and have no fallback override.

See Markdown authoring for mappings, limits, compatibility changes and the distinction between offline fixtures and live editor checks.

• This server uses Substack's unofficial API. It may break if Substack changes their endpoints.
• Session tokens are sent as cookies. Keep your SUBSTACK_SESSION_TOKEN secure.
• The server checks your credentials on startup, after the MCP handshake completes, and only warns — it never blocks startup on a network call. Tools still error individually if the token is expired, which is where the failure is actionable.
• SIGTERM and SIGINT are handled: the server closes its transport and exits 0, so docker stop returns promptly instead of waiting out the grace period.

For opt-in live read checks, see live contract evidence. The probe is disabled in ordinary CI and never publishes or writes.

Before releasing, run npm run test:package. It installs the built tarball with production dependencies in a clean temporary directory, checks both executable entrypoints, and verifies the MCP version and the complete registered tool catalog without real credentials.

git clone https://github.com/conorbronsdon/substack-mcp.git
cd substack-mcp
npm install
npm run build

Run locally:

SUBSTACK_PUBLICATION_URL=https://yourblog.substack.com \
SUBSTACK_SESSION_TOKEN=your-token \
SUBSTACK_USER_ID=your-id \
npm start

Issues and pull requests are welcome. Because this server uses Substack's unofficial API, the most useful contributions are fixes when an endpoint changes. If a tool stops working, open an issue with the tool name and the error. The safe-by-design boundary stays: no publish, no delete, no schedule for long-form posts. Notes publish immediately by design and must keep saying so loudly in their descriptions.

Built and maintained by Conor Bronsdon for the Chain of Thought podcast production workflow, where it drafts and reviews newsletter posts before a human hits publish. Conor hosts Chain of Thought, a show about AI infrastructure and how practitioners actually build with it. More tools for creators live in ai-tools-for-creators. Find Conor on X at @ConorBronsdon.

Companion tools:

• Transistor-MCP: manage podcast episodes, analytics, and transcripts on Transistor.fm
• podcastindex-mcp: search the Podcast Index and track guest appearances
• op3-mcp: report downloads, listener geography, and apps from OP3
• apple-podcasts-mcp: pull plays, followers, and per-episode listening from Apple Podcasts Connect
• gsc-mcp: query search performance, keywords, and sitemaps in Google Search Console
• podcast-benchmark: benchmark a show against its peers using only public data

This is an independent personal project, not affiliated with, sponsored by, or endorsed by any company. All views expressed are my own.

The repository includes a Codex manifest at .codex-plugin/plugin.json and an MCP configuration at .mcp.json. It runs the published npm package over stdio using npx; Node.js and npm must be available. The package version is pinned in .mcp.json, so upgrading the plugin's server is an explicit change.

Configure your Substack credentials outside the plugin using the environment variables or browser-login session described above. Never commit a session token. Installation does not authenticate an account or grant approval to post. Long-form posts remain drafts; Notes publish immediately.

MIT