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buildx_use

Select the active Docker builder for buildx operations. Persist the choice as default for the current context or globally to control which builder subsequent builds use.

Instructions

Select the active builder for subsequent buildx operations.

Without default or global_default the switch applies only to the current CLI session. default persists the choice for the current Docker context; global_default persists across all Docker contexts. Use buildx_list to see available builders and their current status. To avoid switching the global default, pass a specific builder name directly via buildx_build's builder parameter instead. Does not raise on a non-zero CLI exit (a missing buildx plugin or a timeout still raises) - inspect returncode/stderr in the result.

Args: name: Builder name to activate (from buildx_list) default: Persist as default builder for the current Docker context global_default: Persist as default builder across all Docker contexts

Returns: dict: {"returncode": int, "stdout": str, "stderr": str, "truncated": bool}

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
nameYes
defaultNo
global_defaultNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.9.0

TDQS

A4.9/5.0
Behavior5/5

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

The description adds meaningful behavioral context beyond the annotations: it discloses that a non-zero CLI exit does not raise, exceptions for missing plugin/timeout still raise, and the agent must inspect returncode/stderr. It also explains the persistence/storage implications of default vs. global_default, which is not inferable from annotations.

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?

The description is longer than minimum but every section earns its place: opening one-line purpose, scoping semantics, sibling routing, error behavior, and Args/Returns guides. The prose's key points are front-loaded. Minor redundancy exists because the Args section restates persistence semantics already given in the prose, but it serves as a practical quick-reference.

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?

The definition covers the tool's output format, exception behavior, parameter semantics, and relation to siblings, and it explicitly documents the returned dict since there is no output schema. It gives an agent everything required to select and invoke the tool correctly, including which default flags to use and how to handle the result.

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?

The schema has 0% description coverage, yet the description's Args section gives each parameter a concrete meaning: name is the builder from buildx_list, default persists for the current Docker context, and global_default persists across all contexts. This fully compensates for the sparse schema and tells the agent the exact behavioral consequences of each flag.

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?

States a specific verb and resource ('Select the active builder for subsequent buildx operations') and clearly distinguishes itself from siblings by recommending buildx_list for discovery and buildx_build as a direct builder-passing alternative. This resolves ambiguity without needing to inspect other schemas.

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 directs the agent to use buildx_list to see available builders and to pass a builder name via buildx_build when a global default switch should be avoided. The scoping rules for session, Docker context, and all contexts are explicitly stated, giving precise when-and-when-not conditions.

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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