MainStreet website screenshot

MainStreet

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.

MainStreet publishes 1 API on the APIs.io network. Tagged areas include Company, Tax, Tax Credits, Accounting, and Financial Services.

MainStreet’s developer surface includes documentation, getting-started guide, support, engineering blog, pricing, signup flow, changelog, and 14 more developer resources.

🌐 Visit website 📡 Source on GitHub
30.3/100 thin ▬ flat Agent 9/100 agent aware Full breakdown ↓
scored 2026-08-17 · rubric v0.11.0
1 APIs
CompanyTaxTax CreditsAccountingFinancial ServicesSmall BusinessFintechBookkeepingCompliancePayroll

Kin Score

Kin Score Kin Score How this is scored →
scored 2026-08-17 · rubric v0.11.0
Composite quality — 30.3/100 · thin
Contract Quality 0.0 / 25
Developer Ergonomics 9.1 / 20
Commercial Clarity 8.9 / 20
Operational Transparency 2.1 / 13
Governance 1.5 / 12
Discoverability 8.7 / 10
Agent readiness — 9/100 · agent aware
Machine-Readable Contract 0 / 18
Agentic Access Contract 0 / 10
MCP Server 0 / 12
Machine-Readable Auth 10 / 10
Idempotency 0 / 9
Stable Error Semantics 0 / 8
Request/Response Examples 0 / 7
Rate-Limit Signaling 0 / 7
Typed Event Surface 0 / 6
Agent Skills 0 / 5
Well-Known Catalog 0 / 4
Consent & Bot Identity 0 / 3
A2A Agent Card 0 / 8
Dry-Run / Simulate Mode 0 / 4
Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. This rating is computed from github.com/api-evangelist/mainstreet: open an issue to ask a question, or submit a pull request to add artifacts. Want it done for you? Prioritized profiling — $2,500 →

APIs 1

Individual APIs this provider publishes, each with its own machine-readable definition.

MainStreet Identity (OpenID Connect)

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 d...

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Mainstreet Authentication

openIdConnect/oauth2 · 1 scheme

SECURITY

Mainstreet Domain Security

TLSv1.3 · HSTS · DMARC

SECURITY

Scopes 1

OAuth scopes governing access to this provider's APIs.

Mainstreet Scopes

14 scopes · authorizationCode/clientCredentials/implicit/deviceCode

14 scopes

SCOPES

Resources

Get Started 4

Portal, sign-up, and the first successful call

DeveloperPortal
DeveloperPortal
 GettingStarted
GettingStarted
 SignUp
SignUp
 Login
Login

Documentation 1

Reference material describing how the API behaves

Documentation
Documentation

Agent Surfaces 2

MCP servers, agent skills, and machine-readable catalogs

WellKnown
WellKnown
 LLMsTxt
LLMsTxt

Design & Contract 2

Pagination, idempotency, versioning, errors, and events

Conformance
Conformance
 Lifecycle
Lifecycle

Access & Security 3

Authentication, authorization, and security posture

Authentication
Authentication
 OAuthScopes
OAuthScopes
 DomainSecurity
DomainSecurity

Operate 3

Status, limits, changes, and where to get help

Support
Support
 ChangeLog
ChangeLog
 ChangeLog
ChangeLog

Commercial 3

Pricing, plans, and the legal terms of use

Pricing
Pricing
 TermsOfService
TermsOfService
 PrivacyPolicy
PrivacyPolicy

Company 2

The organization behind the API

Website
Website
 Blog
Blog

Other 1

Properties that don't map to a standard resource type

SecondaryMarket
SecondaryMarket

Source (apis.yml)

apis.yml Raw ↑ 
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: '0.20'
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