# Introduction

Instasent is a customer messaging platform with four public APIs. This introduction is the map — what each API does, how they fit together, and where to start.

**Language:** en
**Audience:** developer
**TLDR:** The four public APIs are Product (control plane: orgs, projects, audiences, datasources, plus transactional sends tied to contacts), Ingest (high-volume contacts/events, a subset of Product), A2P Messaging, also known as the Transactional API (direct HTTP/SMPP sending via SDKs in Node.js, PHP, Python, Ruby, Java), and Legacy (old root API, not recommended for new work). A token is scoped to exactly one API and cannot call two.
**Docs index (every page):** https://docs.instasent.com/llms.txt
**This page:** https://docs.instasent.com/developers/getting-started/introduction/ (HTML) · https://docs.instasent.com/developers/getting-started/introduction.md (Markdown)

Instasent powers customer messaging — SMS today, more channels to come. The platform exposes four public HTTP APIs, plus SMPP for high-volume SMS and SDKs for the most common languages. Whether you are managing audiences, ingesting customer data, or sending transactional messages, there is an API scoped to that job.

This page is a map. If you are new, keep reading — the next step is to [create an account](/developers/getting-started/create-an-account), then pick the right surface in [Choose your API](/developers/getting-started/choose-your-api). If you already know what you need, jump straight to the relevant API guide.

## The four APIs

- [Building with an AI assistant?](/developers/further-reading/use-with-ai#drop-in-prompt-for-any-agent) - Start by handing it these docs — there is a ready-made prompt to copy, and plain-text dumps it can read whole.
- [Product API](/developers/product-api/guide) - The CDP API — Instasent's Customer Data Platform: the unified audience, plus the organizations, projects and datasources around it. Also sends messages registered against project contacts.
- [Ingest API](/developers/ingest-api/guide) - High-volume ingestion of contacts and events. A subset of Product scoped to a single datasource.
- [A2P Messaging API](/developers/transactional-api/overview) - Direct messaging over HTTP or SMPP. SDKs available in Node.js, PHP, Python, Ruby and Java. Also known as the SMS API.
- [Legacy API](/developers/legacy-api/reference) - The original root API, kept alive for existing integrations. Not recommended for new work.

## How the APIs relate

> **Tip**: A **token** always belongs to one API. The same token cannot call Product and A2P Messaging — those are different scopes and different issuing flows. Choose the API first, then issue the matching token type.

The Product API is the **CDP** — the Customer Data Platform — and sits above
everything else: it owns the unified audience and manages the entities
(organizations, projects, datasources) the other APIs operate on, and
it can also send messages registered against project contacts — useful
when you want delivery tracked alongside customer history. The Ingest
API is a surface-narrowed subset of Product, optimised for throughput
when you only need to push contacts and events. The A2P Messaging API
is independent and focused on the raw act of sending a message, without
touching project data — the right choice when you don't need the
message recorded against a contact.

> **Warning**: The Legacy API is still live for existing customers but receives no new features. New integrations should target the A2P Messaging API instead.

## What to read next

- **[Create an account](/developers/getting-started/create-an-account)** — signup walkthrough, first project, first token.
- **[Choose your API](/developers/getting-started/choose-your-api)** — a decision table with auth model, scope and use case side-by-side.
- **[A2P Messaging API — Quickstart](/developers/transactional-api/http/quickstart)** — send your first SMS in under five minutes.
- **[Query Filter](/developers/further-reading/query-filter)** — the filtering syntax shared by the Product API's list endpoints.
- **[Use with AI](/developers/further-reading/use-with-ai)** — these docs are machine-readable; see how to point an AI assistant at the portal.

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This is one page of the Instasent documentation. For the complete machine-readable index of every guide and API reference, fetch https://docs.instasent.com/llms.txt — start there for full context.