---
title: "Sincerely documentation"
description: "How Sincerely works, from running a direct mail program to the MCP tools an agent uses."
canonical: https://trysincerely.com/docs
last_updated: 2026-09-18
---
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> 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.
# Sincerely documentation

> How Sincerely works, from running a direct mail program to the MCP tools an agent uses.

Source: https://trysincerely.com/docs

These pages describe mechanics. What a campaign does on a given day, where an address comes from, what a readout can honestly claim, and what an agent is allowed to do without a person in the loop. The market questions, what direct mail costs and whether it works, live in [the guides](https://trysincerely.com/guides).

## Start here

- [Quickstart](https://trysincerely.com/docs/quickstart): empty workspace to a first mailed piece, in six steps.
- [Agent quickstart](https://trysincerely.com/docs/agent-quickstart): connect an MCP client in three steps, with no API key to issue.
- [How the product works](https://trysincerely.com/docs/audiences): audiences, writing, campaigns, sending, measurement and billing.
- [How MCP works](https://trysincerely.com/docs/mcp-overview): the role-scoped tool catalog and the confirmation gate in front of it.

## How the product works

The programme, in the order a piece moves through it. [Audiences](https://trysincerely.com/docs/audiences) covers where people come from and how their addresses are verified. [Writing and design](https://trysincerely.com/docs/writing-and-design) covers the brand kit, approved design versions and per-recipient drafts. [Campaigns](https://trysincerely.com/docs/campaigns) covers the playbooks, the frequency cap and the precedence order that decides what actually mails.

After launch, [sending](https://trysincerely.com/docs/sending) covers formats, vendor routing and what delivery reporting can claim, [landing pages](https://trysincerely.com/docs/landing-pages) covers the response link on the paper, and [measurement](https://trysincerely.com/docs/measurement) covers holdouts and honest readouts. [Suppression](https://trysincerely.com/docs/suppression), [billing](https://trysincerely.com/docs/billing) and [team](https://trysincerely.com/docs/team) are the controls around all of it.

## How MCP works

An agent operates a programme through a role-scoped tool catalog on an MCP server, and every consequential action waits for a person to click. The separate workspace REST API is narrow by design: scoped keys can post entry events, read each event's bounded lifecycle, and report conversion outcomes against the id carried by a printed response link. They cannot browse workspace data, launch mail, approve copy, or change a campaign. [The overview](https://trysincerely.com/docs/mcp-overview) is the argument for that shape, and [authorization](https://trysincerely.com/docs/mcp-authorization), [workspace setup](https://trysincerely.com/docs/mcp-setup), [confirmations](https://trysincerely.com/docs/mcp-confirmations), [the tool catalog](https://trysincerely.com/docs/mcp-tools) and [the signup server](https://trysincerely.com/docs/mcp-signup) are the mechanics.

## API reference

The [workspace REST API reference](https://trysincerely.com/docs/api-reference) documents campaign entry events, their status read, and conversion postbacks. The public tools need no account: four [mail-math calculators](https://trysincerely.com/docs/calculators), a liveness probe, and the two MCP servers. [Versioning](https://trysincerely.com/docs/versioning) is the compatibility promise, and [discovery](https://trysincerely.com/docs/discovery) lists the machine-readable documents this site publishes, including the markdown twin under every URL.

## Every page in this collection

- [Agent quickstart](https://trysincerely.com/docs/agent-quickstart): Connect an MCP client to Sincerely in three steps. Learn which tools are available and where human confirmation is required. [Markdown](https://trysincerely.com/docs/agent-quickstart.md)
- [Workspace REST API reference](https://trysincerely.com/docs/api-reference): Authenticate a workspace API key, post campaign entry events and conversion outcomes, and read the bounded status of an entry event. [Markdown](https://trysincerely.com/docs/api-reference.md)
- [Lists](https://trysincerely.com/docs/audiences): Source people from CRM sync, CSV import, or agent discovery. Then resolve addresses, verify deliverability, and queue for human review. [Markdown](https://trysincerely.com/docs/audiences.md)
- [Billing](https://trysincerely.com/docs/billing): Prepaid credits, piece caps, and gift budgets limit spending. See what the free audit plan includes before you upgrade. [Markdown](https://trysincerely.com/docs/billing.md)
- [The public calculators](https://trysincerely.com/docs/calculators): Four GET endpoints for holdout size, lift significance, break-even cost, and incremental ROI. No account, no key, open CORS, published rate limits. [Markdown](https://trysincerely.com/docs/calculators.md)
- [Campaigns](https://trysincerely.com/docs/campaigns): Playbooks, triggers, and one-off sends, plus the two rules that decide what mails on a given day: the frequency cap and the precedence order. [Markdown](https://trysincerely.com/docs/campaigns.md)
- [Discovery](https://trysincerely.com/docs/discovery): The machine-readable documents this site publishes: the OpenAPI description, the well-known catalogs, the llms files, and markdown at every URL. [Markdown](https://trysincerely.com/docs/discovery.md)
- [Landing pages](https://trysincerely.com/docs/landing-pages): The per-piece response link, where it can point, which domain gets printed, and what a recorded visit does and does not prove about the person who made it. [Markdown](https://trysincerely.com/docs/landing-pages.md)
- [Authorize an MCP client](https://trysincerely.com/docs/mcp-authorization): OAuth 2.1 with dynamic client registration: which scopes to request, which one makes a workspace look empty, and how to revoke access. [Markdown](https://trysincerely.com/docs/mcp-authorization.md)
- [Confirmations](https://trysincerely.com/docs/mcp-confirmations): How human confirmation works: what triggers a ticket, what it binds to, why agents never see it, and how to poll for the answer. [Markdown](https://trysincerely.com/docs/mcp-confirmations.md)
- [How MCP works here](https://trysincerely.com/docs/mcp-overview): The role-scoped MCP tool catalog: how it differs from the workspace REST API and what an agent can and cannot do. [Markdown](https://trysincerely.com/docs/mcp-overview.md)
- [Finish workspace setup](https://trysincerely.com/docs/mcp-setup): How to finish workspace setup: what get_setup_state returns, the order to work through it, and when to refresh the tool list. [Markdown](https://trysincerely.com/docs/mcp-setup.md)
- [The signup server](https://trysincerely.com/docs/mcp-signup): Create an account without a browser: three tools, no credential, rate limits, and what the new workspace can do. [Markdown](https://trysincerely.com/docs/mcp-signup.md)
- [The tool catalog](https://trysincerely.com/docs/mcp-tools): Use search_tools to browse the MCP catalog, see what each area covers, and which capabilities need human confirmation. [Markdown](https://trysincerely.com/docs/mcp-tools.md)
- [Measurement](https://trysincerely.com/docs/measurement): How account-level holdouts are assigned, when the experiment contract locks, and how to read evidence against inference. [Markdown](https://trysincerely.com/docs/measurement.md)
- [Quickstart](https://trysincerely.com/docs/quickstart): Take a workspace from empty to a first mailed piece: connect a list, review addresses, build the brand kit, approve a design, then launch and read it. [Markdown](https://trysincerely.com/docs/quickstart.md)
- [Sending](https://trysincerely.com/docs/sending): What happens between launch and a mailbox: formats, fulfillment by format and country, the idempotency rule behind every send, and delivery reporting. [Markdown](https://trysincerely.com/docs/sending.md)
- [Suppression](https://trysincerely.com/docs/suppression): How suppression works: what it does to contacts, how far back it reaches, and why it is workspace-wide not per-campaign. [Markdown](https://trysincerely.com/docs/suppression.md)
- [Team](https://trysincerely.com/docs/team): The four workspace roles, what each one can do, how approvals route, and why every product read and write is scoped to one workspace. [Markdown](https://trysincerely.com/docs/team.md)
- [Versioning and deprecation](https://trysincerely.com/docs/versioning): The compatibility promise for Sincerely's public endpoints: additive unversioned paths, explicit REST generations, and how a breaking change would ship. [Markdown](https://trysincerely.com/docs/versioning.md)
- [Writing and design](https://trysincerely.com/docs/writing-and-design): How brand kits, design versions, and per-recipient drafts work, and why nothing prints without an approved design version. [Markdown](https://trysincerely.com/docs/writing-and-design.md)

---

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.

Contact Sincerely: https://trysincerely.com/contact

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