Does this image tag exist, and is it supported?

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the description's job is to add behavior. It does: fallback to nearest real tags when a tag is missing, digest and pinned reference output, last-rebuild limited to Docker Hub, EOL status of runtime and OS with an upgrade tag, and the explicit list of supported registries.

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

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

It is a single dense sentence that leads with the scope and then lists outputs, so nothing is wasted. Slightly run-on and output-heavy, but it front-loads the most decision-relevant information.

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

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

An output schema exists, so return values need not be explained, yet the description still usefully summarizes them. Combined with annotation coverage and the registry list, an agent has enough to call the tool correctly; only the missing when-to-use versus check_dockerfile is a gap.

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

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

Schema coverage is 50%: the platform parameter is documented in the schema, but images has no schema description. The description partially compensates by giving concrete image-reference examples (node:20-alpine, ghcr.io/org/app:1.2) that clarify the expected string format, so a baseline 3 is appropriate.

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

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

The description names the exact resource (container image references) with concrete examples (node:20-alpine, ghcr.io/org/app:1.2) and enumerates what is answered: tag existence, digest, pinned reference, platforms, rebuild time, EOL status. It is clearly distinguishable from the sibling check_dockerfile, which operates on Dockerfiles rather than registry image references.

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

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

Usage is implied by the input shape: hand it an image reference and it reports whether the tag exists. However, there is no explicit when-to-use statement, no mention of the sibling check_dockerfile, and no guidance on when this is preferable to inspecting a Dockerfile or registry directly.

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