aid: mainstreet
name: MainStreet
description: 'MainStreet is a US small-business tax-credit and back-office platform
  that identifies, calculates, and files R&D tax credits alongside a client''s CPA.
  Its service covers qualified research expense (QRE) identification under IRC §41,
  the IRS four-part test, business-component documentation, Form 6765 preparation
  (including the mandatory Section G component-level reporting that begins with tax
  years starting after 31 December 2025), the §41(h) payroll-tax offset for
  pre-revenue startups, and state R&D credits across 30+ states. Beyond R&D it claims
  SECURE Act retirement-plan credits, the Small Business Health Care Tax Credit, and
  the Disabled Access Credit, and it sells adjacent back-office services — entity
  formation, banking, expense tracking, and bookkeeping and tax filing. MainStreet
  was founded in 2019 as a venture-backed R&D tax-credit fintech and was acquired by
  Employer.com in May 2025; the brand now operates as part of that back-office suite.
  MainStreet ships no public product API, developer portal, or OpenAPI definition —
  it is an API consumer (payroll data via Finch, document generation via Anvil) rather
  than an API producer. Its only public machine-readable contract is the OpenID
  Connect and RFC 8414 discovery pair served by its identity host.'
url: https://raw.githubusercontent.com/api-evangelist/mainstreet/refs/heads/main/apis.yml
image: https://www.mainstreet.com/opengraph.jpg
x-type: company
x-source: harvest:secondary-market
x-tier: profiled
x-tier-reason: enrichment-pipeline
specificationVersion: '0.23'
created: '2026-08-04'
modified: '2026-08-04'
tags:
- Company
- Tax
- Tax Credits
- Accounting
- Financial Services
- Small Business
- Fintech
- Bookkeeping
- Compliance
- Payroll
apis:
- aid: mainstreet:identity
  name: MainStreet Identity (OpenID Connect)
  description: 'The OpenID Connect / OAuth 2.0 authorization surface behind MainStreet
    sign-in, served from login.mainstreet.com on an Auth0 tenant. It publishes a
    complete OIDC Discovery 1.0 document and an RFC 8414 authorization-server metadata
    document anonymously, advertising authorization-code (with PKCE S256), client
    credentials, refresh token, implicit, password, device code, token exchange and
    JWT bearer grants, DPoP, back-channel logout, and dynamic client registration.
    This is identity infrastructure for MainStreet''s own client portal and bookkeeping
    app — it is not a product API and MainStreet does not document it as a developer
    integration point.'
  humanURL: https://login.mainstreet.com/.well-known/openid-configuration
  baseURL: https://login.mainstreet.com
  tags:
  - Authentication
  - Authorization
  - OpenID Connect
  - OAuth
  - Identity
  properties:
  - type: OpenIDConnect
    url: https://login.mainstreet.com/.well-known/openid-configuration
  - type: Authentication
    url: authentication/mainstreet-authentication.yml
  - type: OAuthScopes
    url: scopes/mainstreet-scopes.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: Website
  url: https://mainstreet.ai/
- type: DeveloperPortal
  url: https://mainstreet.ai/knowledge-hub/
- type: Documentation
  url: https://mainstreet.ai/knowledge-hub/library/
- type: GettingStarted
  url: https://mainstreet.ai/rd-credit.html
- type: Support
  url: https://help.mainstreet.com/
- type: Blog
  url: https://mainstreet.ai/articles.html
- type: Pricing
  url: https://mainstreet.ai/pricing.html
- type: SignUp
  url: https://dashboard.mainstreet.com/welcome
- type: Login
  url: https://login.mainstreet.com/u/login
- type: TermsOfService
  url: https://mainstreet.ai/terms.html
- type: PrivacyPolicy
  url: https://mainstreet.ai/privacy.html
- type: ChangeLog
  url: https://mainstreet.ai/updates.html
- type: ChangeLog
  url: changelog/mainstreet-changelog.yml
- type: Authentication
  url: authentication/mainstreet-authentication.yml
- type: OAuthScopes
  url: scopes/mainstreet-scopes.yml
- type: WellKnown
  url: well-known/mainstreet-well-known.yml
- type: LLMsTxt
  url: llms/mainstreet-llms.txt
- type: Conformance
  url: conformance/mainstreet-conformance.yml
- type: Lifecycle
  url: lifecycle/mainstreet-lifecycle.yml
- type: DomainSecurity
  url: security/mainstreet-domain-security.yml
- type: SecondaryMarket
  url: https://forgeglobal.com/mainstreet_stock/
x-enrichment:
  date: '2026-08-04'
  status: enriched
  artifacts_added: 10
  pass: local-v1