What we tested
Probed live on 23 Aug 2026 against rubric v1. 4 of 5 checks passed.
PROBE-VERIFIEDtier 2 of 3
✓Markdown negotiationAccept: text/markdown
—Markdown twin at a predictable URL/page.md
✓llms.txt/llms.txt
✓API catalogRFC 9727
✓MCP server answers/.well-known/mcp/server-card.json → tools/list
What an agent could do here
Read from the page’s own content, with the wording each was drawn from. Inference is kept separate from tested facts — an agent completing the action is tier 3.
UNVERIFIED
query_api“Base URL: https://api.poststack.dev”https://api.poststack.dev
Context
12 sites in the index share the category email api, of which 2 are transactional.
How we grade
Three tiers. Every listing shows which one it has reached, and when. The rubric.
tier 1Declared
The site says agents are welcome in its robots.txt. A permission, not a capability.
tier 2Probe-verified
We fetched the site and tested each signal ourselves. Dated, repeatable, re-checked on a schedule.
tier 3Behaviourally verified
An agent completed the action end to end — booked, bought, submitted — and it worked.
Own this site?
1 check did not pass when we last looked: Markdown twin at a predictable URL. Each is a small, specific fix; the rubric says exactly what we look for.
Behavioural verification — an agent completing your booking, purchase or contact flow end to end, with the date published here — opens to a small founding cohort first. Leave an email to be in it.
Related verified sites
SendmuxSendmux provides an email API for AI agents to send, receive, route, and manage email inbo
email api ResendResend provides an email API for developers to send transactional and marketing emails at
email api ResendResend provides an email API for developers to send transactional and marketing emails at
email api OpenMailOpenMail provides an email API for AI agents to create inboxes, send and receive emails wi
email api IndiePitcherIndiePitcher provides documentation for sending transactional and marketing emails via SDK
email api docsDocumentation for Kurrier email API service explaining setup and sending email via provide
email api SendKitSendKit provides an email API with SDKs for multiple languages to send transactional email
email api SendPost DocsSendPost provides API and SMTP relay for sending, tracking, and analyzing emails with adva
email api Record generated from a live database query. Method: about the index.