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image_save

Save a Docker image as a tar archive, preserving layers and tags for restoration. Choose to write directly to a host file or return the archive bytes in-band.

Instructions

Save an image as a tar archive: to a file on the server host, or in band.

The archive keeps layers, tags, and metadata so image_load can restore it — different from container_export, which flattens one container's filesystem. With dest_path the archive streams straight to disk (no byte cap), so it handles large images — the file is written by the server's user, ~ is expanded, and an existing file is refused unless overwrite=True. Without dest_path the tar bytes are returned in band, capped at max_bytes (default 32 MiB) because MCP base64-encodes them — a fallback for when no writable host path exists (e.g. a containerized server without a bind mount).

args: id_or_name - Image name or id dest_path - Destination path on the server host; omit to return the bytes in band named - Whether to retain repository/tag names in the saved archive overwrite - Replace dest_path if it already exists (default False) max_bytes - In-band mode: abort with ValueError beyond this many bytes (default 32 MiB) returns: bytes | dict - the tarball bytes (in band), or {"path": , "bytes_written": int}

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
namedNo
dest_pathNo
max_bytesNo
overwriteNo
id_or_nameYes

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior5/5

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

Annotations indicate readOnlyHint=false and destructiveHint=false, but the description adds valuable behavioral context: file overwrite refusal, server user writing, ~ expansion, and in-band byte cap rationale. No contradictions with 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 well-structured with clear paragraphs for overall purpose, mode explanations, and argument list. It is slightly lengthy but every sentence adds value; could be tightened slightly.

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 the tool's complexity (5 parameters, two modes, output schema present), the description thoroughly covers return types, mode behavior, error conditions, and parameter defaults. It is complete and leaves no significant gaps.

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?

Schema description coverage is 0%, yet the description explains all 5 parameters in detail: id_or_name, dest_path (mode-dependent behavior), named, overwrite (refuse unless true), max_bytes (default 32 MiB, reason for cap). This fully compensates for schema's lack of description.

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 tool saves an image as a tar archive and explicitly differentiates from container_export by noting it preserves layers, tags, and metadata for restore via image_load. This distinguishes it from many sibling image_* and container_* tools.

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?

The description provides explicit guidance on when to use each mode (with dest_path for large images, without dest_path for in-band fallback) and contrasts with container_export. It covers prerequisites like writable host path and byte caps.

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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