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mc_join_server

Join a Minecraft multiplayer server by address. Automatically disconnects from the current world, accepts resource packs, and waits until the player is in-world before returning.

Instructions

Join a multiplayer server by address ("host" or "host:port"). Disconnects from the current world/server first if needed, so this changes the user's play session — don't point it at a new server without being asked. The server's resource pack is pre-accepted by default so the join doesn't stall on the confirmation prompt.

The bridge ack means the connect attempt has started — current bridges defer it until the client has settled (no startup/reload overlay), so a join issued right after client launch is safe and may take some extra seconds to ack. By default this also polls until the player is actually in-world: success when a game snapshot shows a player, failure when a DisconnectedScreen appears (its title is returned as the reason). When called from inside a world, the poll first waits for the old session to drop so a stale snapshot of it can't masquerade as the new join. Set wait=false to just fire the join and return.

For repeated automated test runs, prefer a local throwaway server over a live community server — live servers have nondeterministic worlds, other players, and rules about automation.

Requires session_control_enabled=true in the DebugBridge config.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
waitNoPoll until in-world / disconnected before returning. Default true.
addressYesServer address, "host" or "host:port" (e.g. "localhost:25565")
timeoutSecondsNoHow long to wait for the join to complete. Default 60.
acceptResourcePacksNoPre-accept the server resource pack. Default true.
Behavior5/5

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

With no annotations, the description fully discloses behavior: disconnects current session, pre-accepts resource packs, bridge ack mechanism, polling logic, and handling of wait flag. No contradictory statements.

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

Conciseness4/5

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

Well-structured with front-loaded purpose and logical breakdown of behaviors. While detailed, some paragraphs (e.g., bridge ack) could be slightly more concise, but overall efficient for required depth.

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 4 parameters and no output schema, the description fully covers tool behavior, side effects, prerequisites, and success/failure indicators (snapshot vs DisconnectedScreen). No gaps for agent understanding.

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

Parameters4/5

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

Schema coverage is 100% with descriptions, but the description adds meaningful context for parameters like 'wait' (explains polling behavior) and 'acceptResourcePacks' (pre-accepted by default). Adds value beyond schema.

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?

Clearly states 'Join a multiplayer server by address', provides scope (disconnects current world), and distinguishes from sibling tools like mc_leave_server and mc_connect by specifying the action and side effects.

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

Usage Guidelines5/5

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

Explicitly states when to use (joining a server), when not to (don't point without being asked), and provides specific guidance for automated tests (prefer local server), plus mentions required config setting.

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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