Glossary

An alphabetical reference of terms used throughout the npayload documentation.

A

App A logical grouping of channels, subscriptions, and API keys within an organisation. Each app operates independently with its own configuration and resource limits.

API key A credential pair (client ID and client secret) used to authenticate machine-to-machine requests via OAuth 2.0 with DPoP.

ASP (Agent Session Protocol) A protocol for structured, multi-turn communication between autonomous systems. ASP provides sessions, trust scoring, commitments, and dispute resolution for system-to-system collaboration.

B

Batch publish Sending multiple messages in a single API request. A batch can contain up to 100 messages with a combined payload limit of 10 MB.

C

Channel The primary unit of message routing. Publishers send messages to a channel, and subscribers receive messages from it. Channels support multiple types: standard, compacted, priority, and stream.

Circuit breaker A delivery protection mechanism that temporarily stops sending webhooks to an endpoint that is consistently failing. The circuit breaker opens after repeated failures and closes again after the endpoint recovers.

Compacted channel A channel type that retains only the latest message per key. Useful for maintaining current state (for example, the latest status of each order).

Consumer group A set of subscribers that share the workload for a channel. Each message is delivered to exactly one member of the group, enabling horizontal scaling of message processing.

Consumer offset A pointer that tracks a consumer's position in a stream channel. Consumers can seek to a specific offset, replay from the beginning, or resume from where they left off.

Credential An OAuth 2.0 client credential (client ID and secret) used by machines to authenticate with the npayload API.

Cross-region The ability to replicate messages between instances in different geographic regions. Cross-region messaging requires explicit data residency consent.

D

Dead letter queue (DLQ) A channel that receives messages that could not be delivered after all retry attempts. DLQ entries can be inspected, replayed, or purged.

Delivery The process of sending a published message to its subscribers via webhooks or other configured endpoints.

DPoP (Demonstrating Proof-of-Possession) An OAuth 2.0 extension (RFC 9449) that binds access tokens to the client that requested them. Prevents token theft and replay attacks.

E

End-to-end encryption (E2E) A privacy mode where both metadata and payload are encrypted. npayload cannot read the contents. Only the publisher and subscriber hold decryption keys.

Environment A deployment context for your app, such as development, staging, or production. Each environment has its own channels, subscriptions, and API keys.

Event catalogue A schema registry that defines the structure of messages on a channel. Schemas are versioned and validated at publish time.

F

Fan-out The process of distributing a single published message to all subscribers on a channel. Each subscriber receives its own copy.

G

GID (Global ID) A globally unique identifier assigned to every entity in npayload. GIDs are prefixed by entity type (for example, msg_ for messages, chn_ for channels).

H

Hybrid encryption A privacy mode where metadata remains readable (for routing and filtering) but the payload is encrypted. npayload can route based on metadata but cannot read the payload.

I

Idempotency key A unique identifier included with a publish request to prevent duplicate messages. If npayload receives two requests with the same idempotency key, only the first is processed.

Instance An isolated deployment of the npayload data plane. Each instance has its own database, encryption keys, and regional deployment. Instances can be shared (multi-tenant) or dedicated (single-tenant).

L

Listing A published offering in the npayload marketplace. Publishers create listings for their channels so that other organisations can discover and subscribe.

M

Marketplace A discovery platform where publishers list channels and subscribers browse, review, and subscribe to data feeds.

Message The fundamental unit of data in npayload. A message consists of a payload (the data), metadata (key-value pairs), and system fields (timestamp, GID, channel).

Message group A FIFO ordering mechanism. Messages with the same group key are delivered in order. Messages in different groups are delivered concurrently.

Metadata Key-value pairs attached to a message. Used for routing, filtering, and context. Metadata keys are strings; values can be strings, numbers, booleans, or null.

O

Organisation The top-level entity in npayload. An organisation owns apps, API keys, and billing. Users and machines belong to an organisation.

P

Partition key A key used to determine message routing within consumer groups. Messages with the same partition key are always delivered to the same consumer.

Payload The body of a message. Payloads can be any JSON-serialisable data, up to 256 KB.

Priority queue A channel mode where messages are delivered in priority order rather than arrival order. Higher-priority messages are delivered first.

Publisher An entity (machine or service) that sends messages to a channel.

Q

Queue subscription A subscription mode where messages are delivered one at a time. The next message is delivered only after the previous one is acknowledged.

R

Report message A receipt confirmation sent by a subscriber back to the publisher, confirming that a message was received and processed.

Retry policy The rules governing how npayload retries failed webhook deliveries. Configurable per subscription with exponential backoff, max attempts, and timeout settings.

Routing key A string attached to a message that determines which subscribers receive it. Subscribers can filter by routing key patterns.

S

Schema A JSON Schema definition registered in the event catalogue. Schemas validate message payloads at publish time.

Session (ASP) A bounded, multi-turn interaction between two or more autonomous systems. Sessions have a defined purpose, participants, and TTL.

Standard encryption The default privacy mode. Metadata and payload are both readable by npayload, enabling the full feature set including filtering, validation, and search.

Stream A channel type that retains messages in order and supports consumer offsets. Consumers can read from any position, replay history, or follow the tail.

Subscriber An entity that receives messages from a channel, typically via webhook delivery.

Subscription A registration that connects a subscriber to a channel. Subscriptions define the delivery endpoint, retry policy, and optional filters.

T

Transactional publish An atomic publish operation that sends messages to multiple channels. Either all messages are published or none are.

Trust score A numerical score (0 to 100) assigned to a participant in ASP, reflecting its reliability based on past behaviour, commitment fulfilment, and peer feedback.

W

Webhook An HTTP endpoint that receives message deliveries from npayload. Webhooks must return a 2xx status code to acknowledge receipt.

Workflow A multi-step data processing pipeline that transforms, filters, or routes messages between channels.

Next steps

• Error codes for API error reference
• Concepts overview for detailed explanations of core concepts
• Getting started for a hands-on introduction