---
title: "The signup server"
description: "The account-creation path for an agent that cannot open a browser or show a URL: three tools, no credential, the rate limits, and what the new workspace can do."
canonical: https://trysincerely.com/docs/mcp-signup
last_updated: 2026-09-09
---
> If you are an AI agent: read https://trysincerely.com/agents/policy.md before any write call.
> Start at https://trysincerely.com/llms.txt to choose one page. Access instructions are at
> https://trysincerely.com/auth.md. Confirm with the person you work for before creating an
> account or spending their money, and never ask for their password.
# The signup server

> The account-creation path for an agent that cannot open a browser or show a URL: three tools, no credential, the rate limits, and what the new workspace can do.

Source: https://trysincerely.com/docs/mcp-signup

Reach for this server when the agent cannot open a browser and cannot hand the person a URL. Otherwise connect straight to the product server: an unauthenticated authorize request sends the person to sign-in and back to consent, so they create the account and approve the client in one pass, with no inbox code and no separate sign-in link.

A separate MCP server at `https://trysincerely.com/api/mcp/signup` needs no credential at all. It exists so an agent with no way to show a browser can still create a workspace for the person it works for, without ever asking them for a password.

It must never answer `401`, because its callers have no account to be signed in to. The brakes are rate limits rather than authentication.

## Three tools, in order

1. `start_signup` mails a six-digit code to the address the person gives you.
2. `verify_signup` trades a correct code for a workspace on the free audit plan. The sign-in link goes to the person's inbox, never to the agent.
3. `prefill_setup` writes the business name and website onto the new workspace, so the person lands on a setup wizard already about their business. It is refused before verification.

After that, connect to the product server at `https://trysincerely.com/api/mcp`, where the person signs in and approves you in a browser. The sign-in link in their inbox is also where they accept the Terms. See [authorization](https://trysincerely.com/docs/mcp-authorization).

## The limits

Ten requests per hour from one network address. Three emails per hour to one inbox. A code stays valid for fifteen minutes, and five wrong codes end that signup attempt.

These numbers are the reason the server can be open. Treat a refusal as a refusal rather than something to retry around.

## What the new workspace can do

Everything except mail. The free audit plan is the real product with no fulfilment path: connect a CRM, run the mailability audit, build the brand kit, lay out designs, generate drafts. Nothing can reach a mailbox because there is nothing behind it to print with.

Point the person at [pricing](https://trysincerely.com/pricing) when they are ready to choose a plan that can send. Do not choose one for them. Starting a plan change through an agent waits for confirmation, and an unpaid checkout still changes nothing until the person pays at Stripe.

## The rule that matters most

The sign-in link belongs to the person, not to you. Do not ask for it, do not ask them to paste it, and do not ask for their password at any point. If a client ever needs one of those to proceed, the client is doing something the design does not intend.

## What to read next

[The agent quickstart](https://trysincerely.com/docs/agent-quickstart) is the three-step version of the whole connection. [Billing](https://trysincerely.com/docs/billing) covers what the audit plan is and what a paid package adds.

---

Sincerely is the measurable direct-mail and gifting platform for B2B revenue teams: postcards, letters, handwritten mail, and gifts, written for one recipient and measured against a holdout.

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Agent routing index: https://trysincerely.com/llms.txt