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

Annotations already declare destructiveHint=true, so the safety signal is present; the description adds meaningful semantic behavior for the unlimited case (omit value with operation=set). It does not, however, disclose whether decrement can drive credits negative, whether the change is reversible, or 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?

Two tight sentences front-load the core operation and the unlimited special case. The trailing 'Unkey: POST /v2/keys.updateCredits' endpoint reference is minor filler but does not obscure the meaning.

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?

With only 3 params, full schema coverage, no nested objects, and an annotation covering destructiveness, the description gives enough to invoke the tool correctly. Missing only edge-case behavior (negative balances, error conditions), which is a modest gap for a simple mutation.

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%, so keyId, value, and operation are already documented in the schema. The description restates the unlimited-value rule that the value parameter's own description already covers, adding no new syntax or constraint detail. 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 set (set/increment/decrement) and resource (a key's remaining credits), which clearly separates it from the sibling unkey_update_key that handles key metadata. An agent can identify the operation and target without opening the schema.

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?

Provides an explicit conditional rule: 'Use set with no value for unlimited.' However, it offers no guidance on when to prefer this over unkey_update_key or any prerequisites such as required permissions, so the routing context is only partial.

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