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. 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.
More than an index entry, but the surface is still mostly links rather than artifacts — the cohort most likely to move a full band from modest, well-targeted work.
API Evangelist profiles Substack the way a machine reads it — 4 machine-readable artifacts across 2 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 16.7/100 (emerging), with a separate agent-readiness read of 0/100 (human only). 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.
Kin Score
How this is scored →scored 2026-07-27 · rubric v0.5
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 2
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 RSS Feeds
Per-publication public RSS feeds available at https://{publication}.substack.com/feed for syndication and read-only access to posts.
Security Posture 2
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.
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.
Build 1
SDKs, sample code, and the tooling you integrate with
Access & Security 3
Authentication, authorization, and security posture
Operate 2
Status, limits, changes, and where to get help
Commercial 3
Pricing, plans, and the legal terms of use
Company 6
The organization behind the API
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