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

The annotations already flag the tool as destructiveHint=true, idempotentHint=false, and readOnlyHint=false, so the description does not need to establish that it is a mutation tool. Beyond that, it adds useful policy context the annotations cannot express: limits can only be lowered, a key cannot retag itself, and a child key inherits its parent's tags. It does not explain what happens to existing runs when tags change, but the added constraints are substantial.

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 two sentences with no wasted words. The capabilities come first and the constraints come second, so the important behavior is front-loaded and easy to scan.

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 4-parameter mutation tool with no output schema, this description is nearly complete: it explains which fields are updatable, which limits cannot be raised, and how tags interact with child keys. It lacks only secondary details such as the response shape or whether renaming has side effects; those are not required for correct invocation.

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 100%, so the baseline is 3. The description still adds meaning beyond the schema: it clarifies that monthly_limit_usd can only be lowered through this tool, which the schema does not state, and that tags can only be changed on a key you created. It also implies that label is a rename, which helps an agent map the label field to its effect.

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 a specific verb set and a specific resource: rename, retag, or lower the limit of a key. It clearly describes the three fields this tool can mutate, which distinguishes it from other siblings such as create_key, list_keys, and revoke_key. It does not explicitly name those siblings, so it falls short of full differentiation, but its scope is clear.

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?

It clearly states what this tool can do and what it cannot do: "Keys can't raise limits or change their own tags." Those exclusions tell an agent when to stop and look elsewhere, for example to create a new key with a higher limit. It does not name an explicit alternative tool for those operations, so it is clear but incomplete.

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