A MailBox contains InBox and OutBox queues containing Envelopes.


An Envelope is the core object with which agents communicate. It travels from OutBox to another agent. Envelope objects sent from other agents arrive in the InBox via a connection. An Envelope is a vehicle for messages with four attribute parameters:

  • to: defines the destination address.

  • sender: defines the sender address.

  • protocol_id: defines the id of the protocol.

  • message: is a bytes field which holds the message in serialized form.


Protocols define how messages are represented and encoded for transport. They also define the rules to which messages have to adhere in a message sequence.

For instance, a protocol may contain messages of type START and FINISH. From there, the rules may prescribe that a message of type FINISH must be preceded by a message of type START.

The Message class in the protocols/ module provides an abstract class with all the functionality a derived Protocol message class requires for a custom protocol, such as basic message generating and management functions and serialisation details.

A number of protocols come packaged up with the AEA framework.

  • default: this protocol provides a bare bones implementation for an AEA protocol which includes a DefaultMessage class and a DefaultSerialization class with functions for managing serialisation. Use this protocol as a starting point for building custom protocols.
  • oef: this protocol provides the AEA protocol implementation for communication with the OEF including an OEFMessage class for hooking up to OEF services and search agents. Utility classes are available in the module which provides OEF specific requirements such as classes needed to perform querying on the OEF such as Description, Query, and Constraint, to name a few.
  • fipa: this protocol provides classes and functions necessary for communication between AEAs via the FIPA Agent Communication Language. For example, the FIPAMessage class provides negotiation terms such as cfp, propose, decline, accept and match_accept.


Connections wrap an external SDK or API and manage messaging. As such, they allow the agent to connect to an external service with an exposed Python SDK/API.

The module connections/ contains two abstract classes which define a Channel and a Connection. A Connection contains one Channel, which acts as a bridge to the SDK or API to be wrapped. The Channel is responsible for translating between the framework specific Envelope with its contained Message and the external service.

The framework provides a number of default connections.

  • local: implements a local node.
  • oef: wraps the OEF SDK.


Skills are a result of the framework's extensibility. They are atomic capabilities that agents can dynamically take on board, in order to expand their effectiveness in different situations. A skill can be given permission to read the internal state of the the agent, and suggest action(s) to the agent according to its specific logic. As such, more than one skill could exist per protocol, competing with each other in suggesting to the agent the best course of actions to take.

For instance, an agent who is playing chess, could subscribe to more than one skill, where each skill corresponds to a specific strategy for playing chess. The skills could then read the internal state of the agent, including the agent's observation of the game's state, and suggest a next move to the agent.

A skill encapsulates implementations of the abstract base classes Handler, Behaviour, and Task:

  • Handler: each skill has none, one or more Handler objects, each responsible for the registered messaging protocol. Handlers implement agents' reactive behaviour. If the agent understands the protocol referenced in a received Envelope, the Handler reacts appropriately to the corresponding message. Each Handler is responsible for only one protocol. A Handler is also capable of dealing with internal messages.
  • Behaviour: none, one or more Behaviours encapsulate actions that cause interactions with other agents initiated by the agent. Behaviours implement agents' proactiveness.
  • Task: none, one or more Tasks encapsulate background work internal to the agent.


Main loop

The _run_main_loop() function in the Agent class performs a series of activities while the Agent state is not stopped.

  • act(): this function calls the act() function of all registered Behaviours.
  • react(): this function grabs all Envelopes waiting in the InBox queue and calls the handle() function for the Handlers currently registered against the protocol of the Envelope.
  • update(): this function loops through all the Tasks and executes them.

Decision maker

The DecisionMaker component manages global agent state updates proposed by the skills and processes the resulting ledger transactions.

It is responsible for the agent's crypto-economic security and goal management, and it contains the preference and ownership representation of the agent.


Filter routes messages to the correct Handler via Resource. It also holds a reference to the currently active Behaviour and Task instances.

By default for every skill, each Handler, Behaviour and Task is registered in the Filter. However, note that skills can de-register and re-register themselves.

The Filter also routes internal messages from the DecisionMaker to the respective Handler in the skills.


The Resource component is made up of Registries for each type of resource (e.g. Protocol, Handler, Behaviour, Task).

Message Envelopes travel through the Filter which in turn fetches the correct Handler from the Registry.

Specific Registry classes are in the registries/ module.

  • ProtocolRegistry.
  • HandlerRegistry.
  • BehaviourRegistry.
  • TaskRegistry.