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swarm_join

Joins a Docker Engine to an existing Swarm as a worker or manager using the join token from a manager node.

Instructions

Join this Engine to an existing swarm as a worker or manager.

Fails if the Engine is already part of a swarm. Whether this node joins as a worker or a manager is determined entirely by which token is passed — join_token must be one of the two tokens from swarm_join_tokens, called against any existing manager. advertise_addr only needs setting when this host has multiple network interfaces or is behind NAT (otherwise it is auto-detected from the interface used to reach remote_addrs); it must be reachable by every other node in the swarm.

args: remote_addrs - Address(es) of existing swarm managers to connect to join_token - The worker or manager join token (from swarm_join_tokens) — determines the role this node joins as listen_addr - Listen address for inter-manager communication advertise_addr - Externally reachable address advertised to other nodes data_path_addr - Address to use for data path traffic returns: bool - True after the engine joins the swarm

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
join_tokenYes
listen_addrNo0.0.0.0:2377
remote_addrsYes
advertise_addrNo
data_path_addrNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description adds significant behavioral context beyond annotations: failure condition, role determination via token, and auto-detection behavior of advertise_addr. No contradictions with annotations (readOnlyHint=false, destructiveHint=false).

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is concise yet comprehensive, with no wasted words. It starts with the main purpose, then logically lists conditions and parameter details. The structure is efficient and front-loaded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 5 parameters (2 required), no output schema, and the complexity of swarm joining, the description thoroughly covers preconditions, parameter semantics, return type (bool), and edge cases (advertise_addr). It is complete for agent invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With 0% schema description coverage, the description fully compensates by explaining each parameter's purpose and behavior (e.g., join_token determines role, advertise_addr auto-detection). It adds meaning beyond the schema's type/defaults.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Join this Engine to an existing swarm'), the specific roles (worker or manager via token), and distinguishes from sibling tools like swarm_init or swarm_leave. The verb and resource are precise.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explains when to use (join to existing swarm), preconditions (fails if already part of a swarm), and how role is determined. It also gives guidance on advertise_addr. However, it does not explicitly list alternative tools, though the context is clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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