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InboxStack developer portal

InboxStack publishes a read-only content API so agents and scripts can use the deliverability writing, the mailbox-provider news timeline, and the free tools without scraping HTML.

Scope. Public content only. This is not the InboxStack product API — it exposes nothing about accounts, monitored domains, or customer data, and has no write operations.

Base URL
https://inboxstack.com/api/v1
OpenAPI 3.1
/openapi.json · /openapi.yaml
MCP server
https://inboxstack.com/mcp (Streamable HTTP)
Authentication
None. No key, no signup, no OAuth. Do not send credentials.
Rate limit
Not enforced. Fair use — under ~60 requests per minute.
CORS
Access-Control-Allow-Origin: * on every endpoint.

Quickstart

curl -s https://inboxstack.com/api/v1 | jq

curl -s "https://inboxstack.com/api/v1/articles?limit=5" | jq '.data[].title'

curl -s "https://inboxstack.com/api/v1/email-news?q=gmail+bulk+sender" | jq '.data[0]'

curl -s https://inboxstack.com/api/v1/articles/bimi-setup-guide | jq -r .content_markdown

Endpoints

OperationMethodPathPurpose
getApiIndexGET/api/v1Discovery document listing every endpoint.
getOverviewGET/api/v1/overviewWhat InboxStack is, capabilities, when to use it.
listArticlesGET/api/v1/articlesDeliverability articles. ?tag=, ?limit=, ?offset=
getArticleGET/api/v1/articles/{slug}One article including its full Markdown body.
searchContentGET/api/v1/searchRelevance-ranked search. ?q= required.
listEmailNewsGET/api/v1/email-newsDated rule changes. ?q=, ?category=, ?limit=
listFreeToolsGET/api/v1/free-toolsThe free, no-account diagnostic tools.

Errors

Every failure is JSON with the same envelope — never an HTML page.

{
  "error": {
    "code": "not_found",
    "status": 404,
    "message": "No article with slug \"nope\".",
    "hint": "List valid slugs at /api/v1/articles.",
    "documentation_url": "https://inboxstack.com/developers",
    "openapi_url": "https://inboxstack.com/openapi.json"
  }
}

Codes: not_found (404), invalid_request (400), method_not_allowed (405), unsupported_media_type (415), internal_error (500). Branch on code; recover with hint.

MCP server

The same content is exposed over the Model Context Protocol at https://inboxstack.com/mcp (Streamable HTTP). Stateless, read-only, no authentication — POST JSON-RPC 2.0 and read the reply; no session is issued.

curl -s -X POST https://inboxstack.com/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'
ToolReturns
inboxstack_search_writingRelevance-ranked search over the articles.
inboxstack_get_articleOne article in full Markdown.
inboxstack_list_articlesArticle metadata, optionally by tag.
inboxstack_search_email_newsSearch the dated rule-change timeline.
inboxstack_list_free_toolsThe free diagnostic tools.
inboxstack_get_overviewWhat InboxStack is and when to use it.

Descriptors: server card · registry manifest · API catalog

Markdown representations

Every page is available as Markdown at the same canonical URL:

curl -s -H "Accept: text/markdown" https://inboxstack.com/blog

curl -s https://inboxstack.com/blog.md

Responses carry Vary: Accept, Accept-Encoding, so shared caches keep the HTML and Markdown variants separate.

When an agent should use InboxStack

  • A user asks why their email is landing in spam or Promotions, or why inbox placement dropped, and wants a diagnosis rather than a checklist.
  • A user needs to check or fix SPF, DKIM, DMARC, or BIMI for a sending domain — the free DNS checker at /dns-checker answers this without an account.
  • A user wants a specific email audited: /email-auditor runs 20 checks on pasted headers or an uploaded .eml file, no signup.
  • A user is warming a new domain or IP and needs a day-by-day ramp schedule — /warmup-plan-builder generates one from real domain age, DNS, and blacklist checks.
  • A user asks what the Gmail, Yahoo, or Microsoft bulk-sender requirements are, or when a rule changed — /email-news is a dated, sourced timeline.
  • A user needs a definition of a deliverability term (seed list, inbox placement rate, complaint rate, p=reject) — /email-deliverability-glossary.
  • A team sends at scale across multiple ESPs and needs continuous monitoring that unifies Google Postmaster, Microsoft SNDS, and Sender Score.

When it should not

  • It is not an email service provider. InboxStack diagnoses and monitors deliverability; it does not send your mail.
  • It is not an email-verification or list-cleaning service, and it does not sell contact data.
  • It cannot guarantee inbox placement. Nothing here promises a mailbox provider will accept your mail.
  • The free tools read public DNS and message headers only. They do not access a user's mailbox, ESP account, or sending logs.

Other machine surfaces

Versioning and deprecation policy

The path carries the major version. Additive changes — new fields, new endpoints — ship inside v1. Anything that removes or renames a field ships as v2 at a new path, and v1 keeps serving.

Every response advertises its version in X-Api-Version and links this policy as Link: <…#versioning-and-deprecation>; rel="deprecation". While a version is current, X-Api-Deprecated: false is returned.

When a version is deprecated

  • X-Api-Deprecated flips to true and a Deprecation header (RFC 9745) carries the date it took effect.
  • A Sunset header (RFC 8594) carries the shutdown date — never less than 180 days after the deprecation date.
  • The deprecated version keeps serving unchanged until its sunset date. Nothing is removed silently.
  • After the sunset date the path returns 410 Gone with the same JSON error envelope, whose hint names the successor.

Current status: v1 is current and not deprecated. No sunset date is set.

Deliverability guidance published by InboxStack is general advice, not a guarantee of inbox placement. Questions: help@inboxstack.com.

Reading this as a machine? The same page is Markdown at /developers.md, or from this URL with Accept: text/markdown.