Substack MCP Server

Inputs:

• title (string): Title of the post
• subtitle (string): Subtitle of the post
• body (string): Body of the post. Plain text becomes one paragraph per line — Markdown is not interpreted, so ## Heading arrives literally. A JSON string of a Substack document also works and is validated against the same schema set_post_body publishes, so an unrecognised node name is an error rather than a silently mangled post.

Returns: {draft_id, is_published}. Pass draft_id to get_draft to read the draft back.

For anything structured — headings, lists, links, code, images, a paywall — use set_post_body after creating the draft: the schema is published there, so the calling model can read the node vocabulary rather than guess at it.

Exposes the same filtering the Subscribers dashboard offers: 48 columns, 18 operators, free-text search, sorting and pagination.

Inputs:

• filters (array, optional): conditions combined with AND, each {column, operator, value}
• search (string, optional): free text matched against subscriber name and email
• sort_by (string, optional): any filterable column
• sort_direction (asc | desc, optional): defaults to desc
• limit (number, optional): 1–100, defaults to 25
• offset (number, optional): for paging

Which operators a column accepts depends on its type:

The columns cover subscriber identity (name, email, country, state, group membership), subscription (type, start/expiry/cancel dates, revenue, Stripe plan, attribution), email engagement (opens and unique opens over 7d/30d/6mo, links clicked, sections) and site engagement (post views, unique posts seen, comments, shares, days active, activity rating). The full list with types reaches the client in the tool's JSON Schema, so a model does not have to guess names.

Returns: {count, returned, limit, offset, subscribers}. count is the total matching the filters regardless of limit, so a call with limit: 1 is a cheap way to size a segment.

Note: engagement columns can be filtered on here but are not part of the records this tool returns — Substack takes the fields it returns from the publication's saved Display settings and ignores a per-request column list. Use export_subscribers to read their values.

There is no OR and no nesting: anything needing OR has to be issued as separate calls.

The way to actually read the engagement metrics list_subscribers can only filter on: email opens over 7d/30d/6mo, unique emails seen, post views, unique posts seen, comments, shares, links clicked, days active and activity rating.

Inputs:

• filters (array, optional): the same conditions as list_subscribers, combined with AND
• search (string, optional): free text matched against subscriber name and email
• columns (array, optional): which columns to include, defaulting to all of them
• max_wait_seconds (number, optional): 1–600, defaulting to 120

Returns: {count, columns, missing_columns, unmapped_columns, export_id, subscribers}, where each subscriber is keyed by column name.

Substack generates the file asynchronously, so the tool creates a subscriber set, requests the export, polls until it is ready and downloads it. A small export lands in a few seconds. If the wait budget runs out the tool says so and names the export_id rather than blocking.

Two caveats, both verified against the live API:

• tag_ids and group_membership cannot be exported. Substack drops them silently rather than failing, so they are reported in missing_columns — asking for all 48 columns returns 46.
• Values arrive display-formatted, not raw: revenue is "€50.00" here and the number 50 through list_subscribers. Dates are ISO strings.

There is no paging: an export covers the whole matching set.

Inputs:

• status (drafts | published | scheduled): which list to read
• search (string, optional): free text matched against title and content
• limit (number, optional): 1–100, defaults to 25
• offset (number, optional): for paging
• sort_direction (asc | desc, optional): drafts and published posts are newest-first, scheduled posts soonest-first

Returns: {status, total, returned, limit, offset, posts}, each post summarised — use get_draft for the full content of an unpublished one.

Inputs:

• draft_id (number): the id returned by list_posts or create_draft_post

Returns: the draft as Substack stores it, body and audience/email settings included.

The only way to write structured content: headings, lists, links, code blocks, quotes, images, buttons and a paywall. create_draft_post takes plain text; this takes the document Substack actually stores, and its schema is published in tools/list so the calling model can read the node vocabulary instead of guessing.

Inputs:

• draft_id (number): the id returned by list_posts or create_draft_post
• body (object): a Substack ProseMirror document — {type: 'doc', content: [...]}

Fifteen node types are accepted: paragraph, heading, bullet_list, ordered_list, list_item, blockquote, highlighted_code_block, code_block, horizontal_rule, captionedImage, button, paywall, youtube2, plus digestPostEmbed, substack_mentions and directMessage passed through unchanged so a document read with get_draft can be written back. Marks: strong, em, code, strikethrough, link.

Returns: {draft_id, nodes}, where nodes counts what was stored by type — so a caller that asked for a paywall can confirm there is one. Validation cannot report a node that was never sent.

Three things worth knowing:

• An image must already be hosted by Substack. image2.src pointing at an external URL is stored but does not render. Use upload_image to re-host one and get a src that works.
• A document may contain at most one paywall. Substack accepts two and renders both, leaving it undefined which one cuts the post, so this tool refuses the second.
• ordered_list numbers from attrs.order, not attrs.start. A list given only start renders from 1 with no error.

Substack's editor uploads images as base64 data URIs to POST /api/v1/image, which answers with a Substack-hosted URL. image2.src in set_post_body and cover_image in update_draft only render such a URL, so this tool is the bridge. Substack itself only re-fetches URLs already in its own storage, so the image is encoded here rather than being handed off.

Inputs — exactly one of url or path:

• url (string): the http(s) URL of an image to download and re-host
• path (string): absolute path to an image file on the machine running this server, read straight from disk with no download
• post_id (number, optional): the post the image belongs to; its effect is unconfirmed

Returns: {id, url, content_type, bytes, width, height} — put url into an image2.src when calling set_post_body, or into cover_image when calling update_draft.

A download is guarded: only http/https, private and loopback hosts are refused after DNS resolution (redirects are re-checked at every hop), the content type must be an image, HEIC is rejected with a note to convert it, and the image may not exceed 10 MB.

A local file is guarded differently, because it has no Content-Type header to trust. The path must be absolute — a relative one would resolve against this server's working directory, not the calling client's — and the type is read from the file's magic bytes rather than its extension, so a non-image with an image extension is caught here instead of at Substack. PNG, JPEG, GIF and WebP are accepted; HEIC and SVG are not. The same 10 MB cap applies, checked against the file size before the file is read. Note that path reads whatever absolute path it is given: if that matters in your setup, do not expose this server to a client you would not trust with your filesystem.

The update is partial: only the fields you pass change, and the body is left alone.

Inputs:

• draft_id (number): the id returned by list_posts or create_draft_post
• draft_title (string, optional)
• draft_subtitle (string, optional)
• audience (everyone | only_paid | only_free | founding, optional)
• write_comment_permissions (everyone | subscribers | only_paid | none, optional): who may comment
• default_comment_sort (best_first | most_recent_first | oldest_first, optional)
• cover_image (string, optional): the social preview image. A URL already on substack-post-media.s3.amazonaws.com or substackcdn.com is used as-is; anything else is downloaded and re-hosted on Substack first, under the same guards as upload_image
• social_title (string, optional): the title used when the post is shared elsewhere
• description (string, optional): the social preview description — not the subtitle
• search_engine_title (string, optional)
• search_engine_description (string, optional)
• slug (string, optional): the post's URL slug

Returns: {draft_id, updated_fields, draft_title, draft_subtitle, audience, is_published, cover_image, cover_image_rehosted_from}. A call with no field to change is refused rather than sent as a no-op. cover_image is the URL that actually landed, which differs from the one passed when it was re-hosted.

Inputs:

• draft_id (number): the id returned by list_posts or create_draft_post
• send (boolean, optional): email the post to subscribers. Defaults to false, unlike the Substack API's own default — the post goes live on the web either way, but an email cannot be recalled, so it has to be asked for explicitly.

Returns: {status, draft_id, post_id, title, slug, canonical_url, emailed, email_sent_at}. emailed is what was asked for; email_sent_at is the server's own record of whether it mailed.

The email intent is written to the draft's should_send_email before publishing, as well as being passed on the publish call. That field is where the dashboard keeps the decision and it defaults to true, so setting only one of the two would risk mailing the whole list if the endpoint reads the draft rather than the request body.

There is no unpublish tool: publishing cannot be undone from this server.

Inputs:

• draft_id (number): the id returned by list_posts or create_draft_post

Returns: {status, draft_id, draft_title}.

Substack deletes drafts and published posts through the same endpoint, so this tool reads the target first and refuses if it is published — removing a live post is irreversible and is left to the dashboard.

Inputs:

• full (boolean, optional): return all 111 fields (~24 KB) instead of the projection. Defaults to false.

Returns: by default a projection — name, subdomain, custom domain, hero text, copyright, sender name, logo, plans, payment state and the community/podcast flags — plus _meta naming how many fields were dropped. The full payload is mostly notification toggles and the raw HTML of the welcome email, terms and privacy pages.

Inputs:

• full (boolean, optional): include the complete subscriptions array. Defaults to false.

Returns: {id, name, handle, bio, photo_url, publications, primary_publication_id, subscription_count}. publications lists every publication the session has a role on, which is how to discover that SUBSTACK_PUBLICATION_URL is not the only one it could be pointed at.

Inputs:

• include_hidden (boolean, optional): include tags not shown in the navigation. Defaults to true.

Returns: {total, returned, tags}, each {id, name, slug, hidden}. Tag ids are UUIDs, not integers — unlike every other id in this API.

Inputs:

• post_id (number): the id from list_posts. Works for drafts too.

Returns: {post_id, count, tags}, each {post_tag_id, name, slug, hidden, association_id}.

The underlying endpoint answers only UUIDs, so this resolves the names against the publication's tag list. Neither get_draft nor list_posts carries tags, so this is the only way to read them back.

Inputs:

• post_id (number): the id from list_posts. Works for drafts too.
• tag_name (string): matched case-insensitively against existing tags
• create_if_missing (boolean, optional): create the tag when no name matches. Defaults to true; set it to false to have a typo reported instead of turned into a new tag.

Returns: {status, post_id, tag, tag_created, association_id} where status is tagged or already_tagged — re-adding a tag the post already has answers a bare 400 upstream, so it is checked first.

Takes a name rather than an id because the ids are UUIDs, which no caller could reasonably hold.

Inputs:

• post_id (number): the id from list_posts
• limit (number, optional): 1–100, defaults to 50

Returns: {post_id, returned, automod_hidden_count, comments}. Each comment carries its author, plain-text body, reaction and reply counts, and its position in the thread (parent_comment_id, depth). Comments withheld by Substack's automod are counted, not merged in — they arrive in a separate array upstream, and dropping them silently would turn "held" into "nobody commented".

Inputs:

• post_id (number): the id from list_posts
• body (string): plain text; Substack converts it server-side

Returns: {status, post_id, comment}.

This is published under your name. The full text is logged at info before the request, since the log is the only record of what was said. This server does not expose deletion, but the comment can be removed from the Substack UI — unlike a restack, a comment does have an id of its own.

Inputs:

• limit (number, optional): 1–500, defaults to 100
• active_only (boolean, optional): exclude paused and expired subscriptions. Defaults to true.

Returns: {returned, pages_fetched, subscriptions}, each with plan, membership_state, is_founding, is_favorite and whether emails are off. Pages internally up to 20 requests and says truncated: true if that bound is what stopped it.

Not to be confused with list_subscribers, which is who subscribes to you.

Inputs:

• limit (number, optional): 1–100, defaults to 20
• after (string, optional): the next_after from a previous response. A timestamp, not an opaque cursor — this endpoint's own cursor field is always null.

Returns: {returned, more, next_after, posts}, each post summarised with its reading state (is_read, read_progress, is_saved). The Inbox sends every post's full body; it is dropped here, so use get_reader_post to read one.

Inputs:

• post_id (number): from list_reader_posts or get_reader_feed
• include_body (boolean, optional): defaults to true

Returns: the post's metadata plus body_html. body_truncated: true means the body was withheld behind a paywall this session does not clear — preview_text still carries the teaser.

The body stays HTML: converting it would mean a new dependency or a regex pass over markup, and a regex HTML converter mangles nested lists and embeds silently.

Inputs:

• tab (string, optional): tab id — for-you (default) or subscribed. Never the display name: those are localized.
• limit (number, optional): 1–50, defaults to 20
• cursor (string, optional): the next_cursor from a previous response
• include_tabs (boolean, optional): also return the available tab ids

Returns: {tab, returned, next_cursor, items}. Each item is a note or a post. non_content_items_skipped counts the "people to follow" blocks Substack mixes into the array, which carry no content at all.

Inputs:

• user_id (number, optional): defaults to SUBSTACK_USER_ID — your own account
• type (all | notes | posts, optional): defaults to all
• limit (number, optional): 1–50, defaults to 20
• cursor (string, optional)

Returns: {user_id, type, returned, next_cursor, items}. When filtering, read_from_profile reports how many entries the page actually held — otherwise "3 notes out of 20 entries read" would look like "this account has written 3 notes".

Inputs:

• comment_id (number): without the c- prefix Substack uses in urls
• include_replies (boolean, optional): defaults to true

Returns: {comment, branch_count, replies_returned, more_branches, next_cursor, branches}. Each branch is a direct reply plus its descendants, with parent_comment_id and depth resolved.

Inputs:

• comment_id (number): the Note to restack, from get_reader_feed or get_profile_feed
• tab_id (string, optional): defaults to for-you

Returns: {status, comment_id, restack_id, note}.

This is public and appears on your profile, and cannot be undone from here: a restack has no id of its own — it surfaces the original Note with context: comment_restack — so there is nothing for this server to delete. Remove it from the Substack UI.

Notes only. Restacking a post is not offered: that call answers 404 even for a published post on your own publication, so a post_id parameter would produce an error that reads as the post being gone rather than as the tool being wrong.

Inputs: none.

Returns: total and recent subscribers, email and app subscribers, ARR, site views and the 30-day email open rate, each with its change where Substack reports one. If one of the underlying endpoints fails the rest are still returned, and the failure is named under errors.

For anything deeper, use get_analytics.

Which post actually grew the list, which was worth most, which cost you subscribers. The dashboard's "Posts" tab, sortable and paged.

Inputs:

• order_by (string, optional): any of the 43 metrics, defaulting to post_date
• order_direction (asc | desc, optional): defaults to desc
• limit (number, optional): 1–100, defaults to 25
• offset (number, optional): for paging the archive

The metrics worth reaching for:

Returns: {total, returned, limit, offset, order_by, order_direction, posts}. total is the whole archive, not the page; order_by and order_direction are echoed so a ranking is never read without knowing what produced it.

Two caveats, both verified:

• There is no date filter. from_date/to_date are ignored by this endpoint — total does not change — so the schema does not offer them. Narrow by sorting and paging instead.
• Ranking by a rate (open_rate, engagement_rate, click_through_rate) descending puts posts with no data first, because null sorts before numbers. The tool does not filter them out, since that would silently answer a different question.

order_by is an enum on purpose: the API answers 200 for a field it does not recognise and returns an arbitrary order, so a typo would produce a ranking that looks authoritative.

Everything behind the dashboard's Stats tabs, as one tool with a report enum rather than seventeen near-identical tools.

Inputs:

• report (string): which report to read — see the table below
• from_date, to_date (string, optional): YYYY-MM-DD. Used only by the reports covering a period, which default to the last 30 days
• limit (number, optional): 1–100, used only by audience_overlap and subscriber_notes

Returns: {report, params, ignored_params, data}. params is what was actually sent, defaults included — the same report answers very differently over a different window, so the numbers mean little without it. ignored_params names anything you passed that the chosen report does not accept, rather than dropping it silently.

Two neighbouring endpoints are deliberately not exposed: audience_insights/location (the subscriber map) and visitor_sources answer 400 even for Substack's own dashboard, so they are broken upstream rather than mis-called.