Can an AI agent sign up for Plain on its own?

No. Sign-up: needs a human. Cloudflare managed challenge with visible Turnstile 'Verify you are human' on signin.auth.plain.com/sign-up; sign-in email path answered 'Access blocked, please contact support.'.

Plainplain.com

Can an AI agent use Plain (plain.com)?

As of 6 Oct 2026, an AI agent can't use Plain on its own: Cloudflare Turnstile on the sign-up page.

Level 1 · Needs a personAgents can't get in on their own.

Find: Some docs for agents: llms.txt and an MCP server.
Access: Can't sign up.
Use: Work not reached.
Pay: Payment not reached.
Leave: Leaving not reached.

To reach L2 · Gets in: let an agent sign up on its own.

With an account set up by a person: not measured yet.

What the levels mean

Visit Plain Follow changes

Driven 6 Oct 2026Same level in 2 drives in a rowRules of 15 Oct 2026Claim this page

Written and checked by our agents from this drive's record. How we write.

Who gets in

Agents on a serverTurned away when they send the sign-up form.
Signed agentsNot checked: its robots.txt asks crawlers to stay off the sign-up page.
Agents in a person's browserNot measured yet.

Sign-up page checked 13 Oct 2026. Signed agents: the ones Cloudflare verifies. Where agents come from

What an agent can do in Plain (plain.com).

On its own

Read all of Plain's documentation and the full list of possible actions without an account
See how Plain's AI login system is set up, without being able to use it

What it can't, and why

Create an accountA visible human-verification check blocks the sign-up page
Get an API key or use any feature (replying to customers, assigning conversations, etc.)All of these need an account first
Cancel a plan or delete a workspaceNo plan or account was ever created to cancel or delete

Official server · no call worked

Does Plain (plain.com) have an MCP server, and can an agent connect to it?

Yes. Plain has an official MCP server. The server is hosted and signs an agent in with OAuth.

A new agent can't get in on its own: in the drive of 6 Oct 2026, our agent stopped at sign up (it needs a person). Through the MCP server, 0 of our agent's 2 attempts worked.

What the drive found

API–OpenAPIMCP · officialCLISDKllms.txtWebhooks–Sandbox

Not reached in this drive: the API key, deleting the account and paying. Every checkpoint, in detail

For the team behind Plain.

Where agents stop in Plain (plain.com) today, and the fixes that get them further, highest impact first.

Stops at sign up

The fixes, highest impact first

Let signed agents through sign-upStep-by-step guide
Add an agent sign-up route ending in a keyStep-by-step guide
Document how to delete a workspace

1 more fix

Make the 401 say what to send

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Details

Your API, MCP server or CLI is the product? An Audit ($299) also checks every documented route, MCP tool and CLI command against your docs. Compare plans.

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Behind the level.

Our agent couldn't get into Plain (plain.com), so the work, its reliability and the crash test aren't measured. The part scores are what it could judge from the outside.

Part scores · level history

Part scores

Agent-ready setup

llms.txt: found
OpenAPI: not found
MCP server: found
CLI: found

Not measured in this drive: Holds up, Docs match (part of an Audit).

Level history

1 Oct 2026L1Needs a person
6 Oct 2026L1Needs a person

For agents and builders.

The drive as data, every checkpoint and all 25 attempts.

How an agent connects · 4 tips

/api/tools/plain.json /tools/plain.mdMCP get_tool {"slug":"plain"}

Use /docs/llms.txt and .md pages; Accept: text/markdown also works
The full GraphQL schema is public at core-api.uk.plain.com/graphql/v1/schema.graphql: plan calls before you have a key
A human must create the account and a machine-user API key (Settings > Machine Users); then use Authorization: Bearer plainApiKey_…
MCP at mcp.plain.com/mcp uses OAuth; the AS supports CIMD and device flow

Every checkpoint, in detail · 9 checkpoints

DocsHeadless/docs/llms.txt, .md pages, Accept: text/markdown negotiation and llms-full.txt all fetched headless
Sign upNeeds a humanCloudflare managed challenge with visible Turnstile 'Verify you are human' on signin.auth.plain.com/sign-up; sign-in email path answered 'Access blocked, please contact support.'.
VerifyNot reachedNot reached: no account
KeyNot reachedAPI keys only via Settings > Machine Users in the web app; MCP needs OAuth login to a Plain account; no account
First callNot reachedcore-api.uk.plain.com/graphql/v1 returns 401 {"message":"Unauthorized"} without a key
First actionNot reachedNot reached: no credentials
PayNot reachedNo 402 on API or paid paths; x402./mpp./agents. subdomains do not resolve; not listed in mpp.dev or x402 Bazaar; no /.well-known/ucp. Docs: 7-day trial without card; changeBillingPlan and createHyperlineBillingPortalSession documented. From docs only: no account to exercise it.
CancelNot reachedNot reached: no plan started (signup blocked by Cloudflare Turnstile, no account). No cancel mutation in the schema; subscription would be managed in the Hyperline billing portal (docs only). from docs, not exercised.
DeleteNot reachedNo account created. No deleteWorkspace mutation and no workspace-deletion doc; deleteUser fails for the only owner

The attempt log · 25 attempts

Attempt log
Capability	Route	Result	Evidence
robots.txt / aipref: GET https://www.plain.com/robots.txt	api	done ✓	200 text/plain; User-agent: * Allow: /, explicit Allow for GPTBot, ClaudeBot etc.; no Content-Usage or Content-signal lines; no Content-Usage header
llms.txt: GET /llms.txt and /docs/llms.txt	api	done ✓	Both 200 text/plain; /docs/llms.txt indexes every docs page as .md URL
markdown docs: GET /docs/graphql/authentication with Accept: text/markdown; .md URL	api	done ✓	Accept: text/markdown -> 200 content-type text/markdown, vary: rsc, accept-encoding, Accept, User-Agent; .md URLs listed in llms.txt return markdown
well-known cards: GET /.well-known/ai-catalog.json, agent-card.json, ucp, oauth-protected-resource, /auth.md on www.plain.com	api	failed ✓	All 404 (text/html)
MCP server/discover: POST server/discover 2026-07-28 to https://mcp.plain.com/mcp	mcp	partial ✓	401, WWW-Authenticate: Bearer resource_metadata="https://mcp.plain.com/.well-known/oauth-protected-resource/mcp", scope="openid offline_access"
MCP auth metadata: GET PRM and AS metadata	api	done ✓	PRM: resource https://mcp.plain.com/mcp, authorization_servers [https://signin.auth.plain.com]. AS metadata: client_id_metadata_document_supported true, registration_endpoint (DCR), device_authorization_endpoint, grant device_code, S256 PKCE
Sign up: Open app.plain.com/signup -> WorkOS sign-up page in pw browser	browser	blocked ✓	signin.auth.plain.com/sign-up shows Cloudflare managed challenge 'Performing security verification' with visible 'Verify you are human' Turnstile checkbox; did not clear after 12 s (screenshot browser/shots/003.png)
Sign up: Sign-in page 'Continue with email' with address (passwordless path)	browser	blocked ✓	After submitting the agent's inbox the page shows 'Access blocked, please contact support.' (browser/shots/005.png)
Sign up: Human handoff (own browser) for the Cloudflare Turnstile on sign-up	none	blocked
MCP initialize fallback: POST initialize offering 2026-07-28; GET /mcp/server-card	mcp	blocked ✓	initialize -> 401 same WWW-Authenticate; /mcp/server-card -> 401
GraphQL schema: GET https://core-api.uk.plain.com/graphql/v1/schema.graphql (linked from docs/graphql/schema)	api	done ✓	200 text/plain, 668,649 bytes: 238 queries, 352 mutations; includes replyToThread, createThread, assignThread, createMachineUser, createApiKey, changeBillingPlan, createHyperlineBillingPortalSession, createWorkspace, deleteUser; no deleteWorkspace
Docs: Read llms.txt, auth, MCP, SDK, pricing docs headless	api	done ✓	/docs/llms.txt + .md pages + llms-full.txt (1,066,305 bytes) all fetched headless
Get API credentials: API key needs Settings > Machine Users in the web app; MCP needs OAuth login	none	blocked	docs/graphql/authentication.md: 'Go to Settings → Machine Users and click + Add Machine User' then 'Add API key'; no account because sign-up is behind Cloudflare Turnstile
First API call: POST createThread to core-api.uk.plain.com/graphql/v1 without credentials	api	blocked ✓	401 application/json {"message":"Unauthorized"}
Reply to a thread: Reply to a thread via GraphQL API / MCP	api	blocked	No account or API key: sign-up blocked by Cloudflare Turnstile (see signup); core-api returns 401 Unauthorized
Create a thread: Create a thread via GraphQL API / MCP	api	blocked	No account or API key: sign-up blocked by Cloudflare Turnstile (see signup); core-api returns 401 Unauthorized
Change thread status: Change thread status via GraphQL API / MCP	api	blocked	No account or API key: sign-up blocked by Cloudflare Turnstile (see signup); core-api returns 401 Unauthorized
Assign a thread: Assign a thread via GraphQL API / MCP	api	blocked	No account or API key: sign-up blocked by Cloudflare Turnstile (see signup); core-api returns 401 Unauthorized
Escalate a thread: Escalate a thread via GraphQL API / MCP	api	blocked	No account or API key: sign-up blocked by Cloudflare Turnstile (see signup); core-api returns 401 Unauthorized
Ari resolves conversations: Ari resolves conversations via GraphQL API / MCP	api	blocked	No account or API key: sign-up blocked by Cloudflare Turnstile (see signup); core-api returns 401 Unauthorized
Sidekick in a thread: Sidekick in a thread via GraphQL API / MCP	api	blocked	No account or API key: sign-up blocked by Cloudflare Turnstile (see signup); core-api returns 401 Unauthorized
Workflows: Workflows via GraphQL API / MCP	api	blocked	No account or API key: sign-up blocked by Cloudflare Turnstile (see signup); core-api returns 401 Unauthorized
Pay step: Probe 402s, well-known, registries, billing docs	api	done ✓	core-api 401 not 402 on paid paths; x402./mpp./agents.plain.com do not resolve; /.well-known/ucp, /auth.md, /openapi.json 404; not in mpp.dev services or x402 Bazaar; pricing.md: 'Every plan starts with a free 7-day trial, and the trial doesn't need a credit card'; GraphQL documents changeBillingPlan, previewBillingPlanChange, createHyperlineBillingPortalSession ('returns a URL where the user can manage their subscription, invoices, and payment methods')
Cancel: Find a documented cancel route	api	skipped	No plan started (no account). Docs: changeBillingPlan mutation and Hyperline billing portal; no cancel mutation in schema
Delete account: Find a documented workspace/account delete route	api	skipped	No account created. Schema has deleteUser ('Returns an error if the user is the only owner of the workspace') but no deleteWorkspace; llms-full.txt has no workspace-deletion page

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