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

Annotations already cover readOnly/idempotent/non-destructive, but the description adds genuinely new behavior: no value is ever accepted, credentials must not transit agent context or transport, the call returns human-facing instructions, single-string vs structured token-set secrets rotate atomically, and the write targets the project DEFAULT with tenant override via REST. That is far beyond the annotation payload.

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 paragraphs, each earning its place, with the single most important constraint ('NO VALUE IS ACCEPTED HERE') front-loaded in caps. Slightly longer than strictly necessary for the atomic-rotation detail, which is why it is not a 5.

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?

There is no output schema, so the description compensates by describing what the call returns (instructions plus the exact key name for a human). Combined with the parameter and safety context, an agent has everything needed to invoke it correctly.

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 nonetheless adds meaning by explaining how the key surfaces at runtime (req.secrets['KEY']) and by clarifying the project_id/DEFAULT-vs-tenant-override semantics that the schema only gestures at.

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 opens with a specific verb+resource+outcome ('Register a credential a project's Functions read at runtime') and immediately distinguishes itself from the sibling set by stating that no value is accepted and that it emits operator instructions. An agent can separate this from set_variable, list_secrets and delete_secret without reading schemas.

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 states the trigger clearly ('Call this to declare which secrets a Function needs, then hand the operator that list') and implies the hand-off workflow. It does not explicitly name an alternative tool or a when-not condition, so it stops short of the top band.

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