Substack
Substack is an independent newsletter and media platform that lets writers, podcasters, video creators, and other culture makers publish directly to readers and monetize through paid subscriptions. Founded in 2017 by Chris Best (CEO), Jairaj Sethi (CTO), and Hamish McKenzie (CWO) and headquartered in San Francisco with a New York City office, Substack provides built-in subscription billing, paid posts, podcasting, chat, video, Notes, and a cross-publication recommendations network. Creators keep 90 percent of subscription revenue (less credit card fees) and own their mailing lists and content. The platform reports more than five million paid subscriptions and tens of millions of weekly active readers. Substack does not offer a general-purpose public REST API for managing publications, posts, or subscribers. It does publish a narrowly scoped official Developer API (released April 2026) that allows token-authenticated lookup of public Substack profiles by LinkedIn handle, gated by an application and Terms-of-Use process. Substack also runs an official remote MCP server at https://mcp.substack.com/api/v1/mcp, documented August 2026, which gives an MCP-capable AI assistant read-only access to publication analytics under OAuth 2.1 with the mcp:read scope, gated to Admins of Bestseller publications. Read access to public content is otherwise available via per-publication RSS feeds, and the broader integration ecosystem relies on reverse-engineered, unofficial JSON endpoints used by the Substack web application. Substack publishes no OpenAPI, no AsyncAPI, no webhooks and no first-party SDK in any package registry.
Limited machine-readable signal and partial portal coverage — documentation a human can read, but little a machine or agent can consume without scraping.
API Evangelist profiles Substack the way a machine reads it — 10 machine-readable artifacts across 3 APIs, pulled from the provider's own public surface and indexed so a developer, an analyst, or an AI agent can evaluate it against every other provider on the network.
Every provider in the network is reduced to the same set of machine-readable artifacts — OpenAPI contracts, event specifications, GraphQL schemas, runnable collections, pricing and rate-limit signals, security posture, OAuth scopes, and the agent surfaces (MCP servers and skills) that let software drive the API on its own. We profile them because the interface is the part of a company you can actually inspect: it is a truer signal of what a provider does than any marketing page. From those artifacts we compute the Kin Score — Substack scores 37.1/100 (thin), with a separate agent-readiness read of 11/100 (agent aware). The full breakdown is below, followed by every artifact we hold — each card links through to its machine-readable definition on apis.io.
Kin Score
This is the API Evangelist rating — a single, repeatable read computed from the artifacts on this page. Green fill is points earned; the red track is points possible, so every bar shows earned-versus-possible at a glance. Every facet and dimension name is a link: it opens that measurement's page on APIs.io, where the rating runs across the whole catalog — the exact checks that feed it, how every profiled provider distributes on it, and who is at the top of it.
Kin Score
How this is scored →scored 2026-09-08 · rubric v0.20.0
Put this on your own site. The badge is drawn live from Substack's current Kin Score — paste it once and it updates itself every time the score is recomputed. It follows your visitor's light or dark setting, and it links back here so anyone who sees it can read the full breakdown.
<!-- Kin Score · API Evangelist -->
<a href="https://providers.apievangelist.com/providers/substack/"
title="Substack on API Evangelist — API profile and Kin Score">
<img src="https://apis.io/badge/substack.svg"
alt="Substack Kin Score — API readiness rating by API Evangelist" width="150" height="150" loading="lazy">
</a>[](https://providers.apievangelist.com/providers/substack/)<!-- Kin Score · API Evangelist -->
<a href="https://providers.apievangelist.com/providers/substack/"
title="Substack on API Evangelist — API profile and Kin Score">
<img src="https://apis.io/badge/substack/card.svg"
alt="Substack Kin Score — API readiness rating by API Evangelist" width="340" height="120" loading="lazy">
</a>More shapes, themes and sizes → · Score as JSON · How badges work
How we profile Substack
Each block below is one kind of artifact we hold for Substack. For each we say what it is and why it earns a place in the profile, then list every one we've indexed — capped at two rows, scroll within the panel for the rest.
APIs 3
Each API is captured as its own OpenAPI definition — every operation, parameter, and response. This is the single most useful machine-readable description of what an API does, and it's what lets us score, lint, mock, and generate against it without asking the provider for anything.
Individual APIs this provider publishes, each with its own machine-readable definition.
Substack Developer API
Narrowly scoped official API that returns public Substack profile data for a given LinkedIn handle. Access requires accepting the Developer API Terms of Use, applying via form, ...
Substack MCP Server
Official remote Model Context Protocol server that connects a Substack publication to an MCP-capable AI assistant (Claude, ChatGPT, Cursor). Read-only: it serves publication das...
Substack RSS Feeds
Per-publication public RSS feeds available at https://{publication}.substack.com/feed for syndication and read-only access to posts. RSS 2.0 with the content, dc, atom and itune...
MCP Servers 1
Model Context Protocol servers expose these APIs directly to AI agents. We profile them because agent-native access is the fastest-growing way this provider's capabilities actually get used.
Model Context Protocol servers that expose these APIs to AI agents.
Substack
MCP SERVERPricing Plans 1
Pricing is part of the interface. Machine-readable plans tell you what a tier costs and includes before you commit — one of the things the Kin Score reads for access clarity — renamed from commercial clarity in rubric 0.12, because a free statutory interface has access terms and no commercial ones.
Published pricing tiers and plan structures.
Rate Limits 1
Rate limits are the difference between a demo that works and a production integration that doesn't fall over. Publishing them is an operational-transparency signal — and a hard requirement for any agent that plans its own throughput.
Documented rate limits and quota policies.
Substack Rate Limits
RATE LIMITSSecurity Posture 3
Authentication, domain security, vulnerability disclosure, and trust-center signals — the evidence that a provider takes security seriously enough to document it. We profile it because you can't govern what you can't see.
Authentication, domain security, vulnerability disclosure, and trust-center signals.
Scopes 1
OAuth scopes are the vocabulary of least-privilege access. Profiling them shows exactly what an integration — or an agent acting on a user's behalf — is allowed to do.
OAuth scopes governing access to this provider's APIs.
Resources
Every other property we hold for Substack — documentation, portals, status pages, policies, and corporate surface — grouped by the job it does, following the integrator's arc from getting started to running in production.
Get Started 2
Portal, sign-up, and the first successful call
Documentation 2
Reference material describing how the API behaves
Agent Surfaces 3
MCP servers, agent skills, and machine-readable catalogs
Design & Contract 5
Pagination, idempotency, versioning, errors, and events
Build 2
SDKs, sample code, and the tooling you integrate with
Access & Security 5
Authentication, authorization, and security posture
Operate 6
Status, limits, changes, and where to get help
Commercial 5
Pricing, plans, and the legal terms of use
Company 7
The organization behind the API
Scroll within the panel for all 7 ·
Other 3
Properties that don't map to a standard resource type
← All providers · Data indexed from github.com/api-evangelist/substack · machine-readable index on apis.io
This is an independent, third-party profile of Substack, published by API Evangelist. We do not operate, host, resell, or support these APIs, and we are not affiliated with or endorsed by the company unless stated above. Everything here is built from publicly available information — the company's own site, developer portal, documentation, public repositories, and the specifications it publishes for public use. Nothing is obtained by breaching a system, defeating an access control, or using credentials.
The Kin Score and Agent Readiness rating are independently calculated assessments of a company's public API artifacts, scored against a published rubric. They are not certifications, endorsements, security assessments, or audits.
Corrections, re-scores, and removal are free — no partnership or purchase required, and you do not need to justify the request. A removed company is recorded as unrated, never scored zero for having asked. Acknowledgement within one business day; removal within two.
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you will get a person, not a form — we will tell you exactly which public URLs this profile was built from.