VI · Multi-AgentExperimental·

Blackboard

also known as Shared Workspace, Collaboration Whiteboard

Give multiple agents a shared, queryable workspace they can read from and write to as they collaborate.

This pattern helps complete certain larger patterns —

  • used-bySOP-Encoded Multi-Agent Workflow★— Encode a human Standard Operating Procedure (roles, ordered phases, standardised hand-off artefacts) into a multi-agent pipeline so that agents communicate through structured documents rather than free-form chat.

Context

Several specialised agents are working on a shared artefact — a document being annotated by a layout-extractor, table-parser, citation-resolver, and summariser; a code review where multiple analysers contribute findings — and each needs to see what the others have already produced before deciding what to do next. The agents are not in a fixed pipeline; the order of useful contributions depends on what is already on the page.

Problem

If the agents work in isolation, they cannot build on each other's findings and duplicate or miss work. If they message each other point to point, every new agent forces edits to every other agent that should hear from it, and the protocol grows into a brittle web. If they share an unstructured mutable workspace without discipline, concurrent writes race and overwrite useful intermediate state. The team needs a coordination shape that is more flexible than a strict pipeline but more disciplined than free shared memory.

Forces

  • Concurrent writes need conflict resolution.
  • Blackboard contents grow; pruning is needed.
  • Read latency: pulling vs subscribing.

Example

A document-processing pipeline has a layout-extractor agent, a table-parser, a citation-resolver, and a summariser, each strong on its own but needing each other's intermediate outputs. Wiring direct messages between every pair becomes a brittle protocol. They adopt a Blackboard: each agent posts its findings to a shared workspace and subscribes to relevant updates, with a controller deciding who runs next. Coordination becomes 'read what's on the board, contribute what you can'.

Diagram

Solution

Therefore:

Establish a shared store (file, database, in-memory). Each agent reads the relevant slice and writes its contribution under structured keys. Optional event notification when keys change. Conflict resolution is policy-driven (last-write-wins, version-vector, append-only).

What this pattern forbids. Cross-agent communication happens only via the blackboard; out-of-band agent-to-agent calls are forbidden.

The smaller patterns that complete this one —

  • generalisesStigmergic Coordination★★— Agents coordinate indirectly by leaving and reading marks in a shared environment (files, queues, scratchpads, world model) so that one agent's trace stimulates another's next action, with no direct messaging.

And the patterns that stand alongside it, or against it —

  • complementsSwarm·— Run many peer agents that interact directly without a central supervisor, achieving emergent coordination.
  • alternative-toSupervisor★★— Place a coordinating agent above a set of specialised agents and route work to them.
  • complementsAppend-Only Thought Stream★— Make the agent's thought log append-only so the agent cannot rewrite its own history.
  • composes-withGraph of Thoughts·— Model reasoning as an arbitrary DAG so thoughts can be merged, refined, and aggregated across branches.
  • alternative-toTopic-Based Routing★— Route inter-agent messages through named topics that agents subscribe to, instead of having senders address each other by id.
  • alternative-toCellular-Automata Agents·— A swarm where each agent applies simple local rules to its immediate neighborhood; macro behavior emerges without a central orchestrator and without global information access.
  • alternative-toDistributed Constraint Optimization·— A group of agents jointly assigns values to shared variables to minimise (or maximise) a global cost defined by inter-agent constraints, exchanging only the messages needed.
  • complementsPartial Global Planning·— Each agent maintains a partial view of others' plans and incrementally merges local plans into a shared partial global plan, interleaving coordination with execution.

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