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

Annotations already declare readOnlyHint=false and destructiveHint=true, so the safety profile is partly covered. The description adds genuinely new behavior: credentials are 'Never returned', which tells the agent that list output cannot expose secrets and that set is a write-only store. It omits confirmation behavior for delete and any auth requirements.

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?

Three short sentences, front-loaded with the purpose, then the payload variants, then the 'Never returned' caveat. No filler or repetition of the schema.

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?

For a 6-parameter mutation/read tool with no output schema, the description covers purpose, per-provider payload formats, and the secrecy of the values. It does not explain list return shape (acceptable, since 'Never returned' covers the security-relevant part) or delete semantics beyond the annotation's destructiveHint.

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 83%, so the baseline is 3, but the description goes further by spelling out the two distinct set payload shapes ({registry, username, password} vs {registry, accessKeyId, secretAccessKey}) and the Google _json_key convention. This tells the agent which parameters are mutually exclusive per provider, information not fully conveyed by flat schema fields.

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?

States specific verbs (list/store/forget) and a precise resource: the credentials builds use to pull private images. An agent can distinguish this from runtime_images_build or runtime_images without opening the schema. It stops short of naming siblings explicitly, but the scope is unambiguous.

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?

The action enum (list/set/delete) is mirrored in prose, so the mapping between operation and tool is implied. However, there is no guidance on when to prefer this over runtime_secrets or runtime_images_build, and no stated prerequisites (e.g., permissions) for storing credentials.

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