# Concepts

> Index of platform concepts — typed refs, accounts, identity and access, rail classes, funding and withdrawal endpoints, conversions, operations, and more.

Source: https://business-api-docs.youhodler.com/docs/concepts

Use concepts when you need the platform model before you read workflows or raw
API reference. This section explains the typed reference system, the nesting of
tenant and financial objects, the canonical operation model, and the control
and delivery surfaces that sit around execution.

These pages are not procedural guides. They are the fastest way to understand
how public resources relate to each other, which identifiers belong where, and
which API surfaces act as topology boundaries, execution boundaries, governance
boundaries, or audit boundaries.

> **How to read this section:** Start with typed refs and accounts if you are still building the integration model. Move into operations, policies, and events when you need to understand how execution, governance, and delivery fit together across the same tenant perimeter.

## Quick Access

### Topology And Refs

Understand how typed refs separate topology boundaries, financial account boundaries, and broader resource references.

- [Mental model](/docs/concepts/topology-and-refs#mental-model)
- [TopologyRef](/docs/concepts/topology-and-refs#topologyref)
- [AccountRef](/docs/concepts/topology-and-refs#accountref)
- [API shape](/docs/concepts/topology-and-refs#how-this-appears-in-the-api)

[View all →](/docs/concepts/topology-and-refs)
### Accounts

Read how master and client accounts hold balances, how available, held, and total split a balance, and where overdraft fits.

- [Balance reads](/docs/concepts/accounts#balance-reads)
- [Overdraft](/docs/concepts/accounts#overdraft)
- [API shape](/docs/concepts/accounts#how-this-appears-in-the-api)

[View all →](/docs/concepts/accounts)
### Identity

Read how human actors, service principals, platform-hosted and federated humans, and on-behalf-of flows establish who is making a call.

- [Actor types](/docs/concepts/identity#actor-types)
- [Human sourcing](/docs/concepts/identity#how-human-actors-are-sourced)
- [Acting on behalf](/docs/concepts/identity#acting-on-behalf-of-a-human)
- [Client-scoped identities](/docs/concepts/identity#client-scoped-identities)

[View all →](/docs/concepts/identity)
### Access

Understand how capabilities, scopes, and role assignments combine into authorization, and how machine-native and human-governed actions differ.

- [Action classes](/docs/concepts/access#action-classes)
- [Capabilities and scopes](/docs/concepts/access#capabilities-and-scopes)
- [Roles](/docs/concepts/access#roles-and-role-assignments)
- [API shape](/docs/concepts/access#how-this-appears-in-the-api)

[View all →](/docs/concepts/access)
### Rail Classes

Read the fiat-vs-crypto contract that governs how funding endpoints, withdrawal destinations, and deposit instructions are configured and routed.

- [Where it appears](/docs/concepts/rail-classes#where-rail-class-appears)
- [Routing pair](/docs/concepts/rail-classes#the-routing-pair-pattern)
- [API shape](/docs/concepts/rail-classes#how-this-appears-in-the-api)

[View all →](/docs/concepts/rail-classes)
### Funding Endpoints

Define the durable inbound routes for a tenant: which rail, which asset, and how the platform tags inbound activity back to the right perimeter.

- [Mental model](/docs/concepts/funding-endpoints#mental-model)
- [Lifecycle](/docs/concepts/funding-endpoints#lifecycle)
- [Related resources](/docs/concepts/funding-endpoints#relationship-to-other-resources)
- [API shape](/docs/concepts/funding-endpoints#how-this-appears-in-the-api)

[View all →](/docs/concepts/funding-endpoints)
### Withdrawal Destinations

Define the durable outbound routes for a tenant: which rail, which asset, and where the platform delivers funds when a withdrawal executes.

- [Mental model](/docs/concepts/withdrawal-destinations#mental-model)
- [Lifecycle](/docs/concepts/withdrawal-destinations#lifecycle)
- [Related resources](/docs/concepts/withdrawal-destinations#relationship-to-other-resources)
- [API shape](/docs/concepts/withdrawal-destinations#how-this-appears-in-the-api)

[View all →](/docs/concepts/withdrawal-destinations)
### Conversions And Pricing

Read the three-layer model that splits conversion discovery, pricing previews, and execution into distinct surfaces with distinct semantics.

- [Mental model](/docs/concepts/conversions-and-pricing#mental-model)
- [Conversion pairs](/docs/concepts/conversions-and-pricing#conversion-pairs)
- [Pricing surfaces](/docs/concepts/conversions-and-pricing#pricing-surfaces)
- [Conversion operations](/docs/concepts/conversions-and-pricing#conversion-operations)

[View all →](/docs/concepts/conversions-and-pricing)
### On-Ramp And Off-Ramp

Coming soon: canonical model for on-ramp and off-ramp operation families, including sessions and settlement records.

- [Why a separate family](/docs/concepts/ramps#why-ramps-are-their-own-family)
- [Canonical layers](/docs/concepts/ramps#canonical-layers)

[View all →](/docs/concepts/ramps)
### Operations

Read the canonical money-movement model that unifies multiple families behind one operation lifecycle and read model.

- [Mental model](/docs/concepts/operations#mental-model)
- [Families](/docs/concepts/operations#family-types)
- [Status](/docs/concepts/operations#lifecycle-status)
- [API shape](/docs/concepts/operations#how-this-appears-in-the-api)

[View all →](/docs/concepts/operations)
### Idempotency And Concurrency

Use `Idempotency-Key` to make creates retry-safe and `If-Match` to make updates concurrency-safe; read both as separate cross-cutting tools.

- [Idempotency](/docs/concepts/idempotency-and-concurrency#idempotency)
- [Concurrency control](/docs/concepts/idempotency-and-concurrency#concurrency-control)
- [When to use which](/docs/concepts/idempotency-and-concurrency#when-to-use-which)
- [API shape](/docs/concepts/idempotency-and-concurrency#how-this-appears-in-the-api)

[View all →](/docs/concepts/idempotency-and-concurrency)
### Policies And Approvals

Coming soon: canonical policy resources and approval cases that gate sensitive operations through the runtime lifecycle.

- [What belongs here](/docs/concepts/policies-and-approvals#what-belongs-here)

[View all →](/docs/concepts/policies-and-approvals)
### Commercial Agreements

Coming soon: versioned configuration that controls how fees apply to operations, split between platform-level and enterprise-level agreements.

- [What belongs here](/docs/concepts/commercial-agreements#what-belongs-here)

[View all →](/docs/concepts/commercial-agreements)
### Events And Webhooks

Separate pull-based audit history from push delivery, and understand how events and webhook endpoints complement each other.

- [Mental model](/docs/concepts/events-and-webhooks#mental-model)
- [Events](/docs/concepts/events-and-webhooks#events)
- [Webhooks](/docs/concepts/events-and-webhooks#webhook-endpoints)
- [API shape](/docs/concepts/events-and-webhooks#how-this-appears-in-the-api)

[View all →](/docs/concepts/events-and-webhooks)