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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds one non-obvious behavioral guarantee that annotations do not carry: values are never returned, which both sets agent expectations and signals the tool is safe to call without exposing secrets. Ordering, pagination and empty-list behavior remain undisclosed.

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?

One sentence, front-loaded with the action, with the most decision-relevant constraint (keys only, never values) in parenthetical emphasis. Nothing is wasted and nothing important is buried.

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 one-optional-parameter read-only tool with no output schema, the description covers the essentials: it returns key names and only key names, which is effectively the return-value contract. Minor gaps (scope of the listing, ordering, behavior with no session) are low-risk given the annotations and full schema coverage.

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 description coverage is 100% and the single project_id parameter is fully documented in the schema, including the 'or use session from use_project' fallback. The description adds nothing beyond that, so the baseline 3 applies.

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 a specific verb and resource (list environment variable keys) and adds a sharp scope qualifier: KEYS only, never values. That qualifier is what separates it from the sibling write-side tool set_env, so an agent can tell the difference without opening the schema, though no sibling is named explicitly.

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?

There is no when-to-use or when-not-to-use guidance. The description never says to call this before set_env, nor how it relates to project_id vs the session established by use_project, which is the one real decision an agent faces here. The keys-only phrasing only hints at intent.

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