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

The annotations already declare destructiveHint=true and idempotentHint=false, and the description adds genuinely useful timing context ('Applies on next restart') that the annotations do not convey. However, it never explains why the operation is marked destructive — e.g. that overwriting loses the previous value or that renaming can break references in deployments — which is exactly the risk an agent needs to weigh before calling.

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?

Two short sentences with no filler; the actionable enumeration of editable fields comes first and the behavioural caveat (restart timing) is placed last where it belongs.

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 destructive, non-idempotent mutation with five undocumented parameters and no output schema, the description is thin. It covers what can be changed and when changes take effect, but omits the id/key/newKey relationship and any warning about the consequences flagged by 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 description coverage is 0% for 5 parameters, so the description must carry the burden and only partially does: it maps newKey to renaming, value to the value change, and secret to the secret flag. Crucially it never explains the distinction between the required 'id' and required 'key' parameters, nor how key relates to newKey during a rename, leaving two required fields ambiguous.

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 gives a specific verb ('Update') plus resource ('an existing environment variable') and enumerates the three mutable facets: rename via newKey, value change, and the secret flag. It implicitly separates itself from env_set by requiring the variable to already exist, though it never names that sibling directly.

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?

'Update an existing environment variable' implies the create path belongs to a different tool (env_set), but that alternative is never named and no exclusion is stated. An agent must infer from the word 'existing' that env_set is the sibling to use for new variables.

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