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

Beyond the annotations, the description discloses the 5-plate cap, idempotent semantics spelled out concretely ('Saving or removing the same plate twice changes nothing'), the auth prerequisite with the exact failure mode (401 with sign-in details), and a no-charge guarantee. These are real behavioral facts an agent cannot derive from readOnlyHint/idempotentHint/destructiveHint alone. Removal being non-destructive is consistent with the annotations because a removed plate can simply be re-saved.

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 front-loaded with what the tool returns, then action semantics, then constraints, then auth and payment caveats, so an agent can stop reading early and still act correctly. It runs long and the closing payment sentence is only indirectly relevant to this read-mostly tool, which keeps it from a perfect score.

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, and the description compensates by describing the shape of the result (up to five labeled plates plus unsaved past plates). With only three simple parameters, full schema coverage, and explicit auth and idempotency behavior, nothing an agent needs to invoke this correctly is missing.

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, but the description adds meaning the schema does not: which actions consume which parameter combinations, that the label is optional per plate, and that a saved plate becomes usable by reserve. The plate normalization rule (spaces and dashes ignored) is already in the schema, so that part earns no extra credit.

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 states a specific resource and scope: the signed-in driver's saved vehicles (capped at 5 plates with optional labels) plus unsaved plates from past parking. It then enumerates the four action modes (list/save/rename/remove) with a one-clause meaning for each, which is enough for an agent to separate this tool from my_sessions or reserve 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?

Usage is mapped per action, including the default ('action list (the default) only reads'), and the description explicitly links the result to a sibling by noting 'A saved plate works as reserve's plate.' It stops short of stating when not to use the tool or naming which sibling to pick for session-level questions, so it is clear context rather than full routing guidance.

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