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

Goes well beyond the annotations by disclosing the concrete return: "one sign-up link with the plate filled in," and the two follow-up steps the user must complete on that page (sign the contest authorization, add a card). It also pre-empts confusion about pricing. It does not say what happens if the plate is already enrolled or ineligible, which keeps it from a 5.

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 sentences, front-loaded with what the tool does, then eligibility context, then return value. The pricing aside is slightly compressed with the return-value sentence but each clause carries information the agent needs to explain the tool to a user.

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 no output schema, the description correctly fills that gap by describing the single return (a sign-up link with the plate pre-filled) and the user's downstream steps. What's missing for a signup/enrollment tool is failure-mode behavior — ineligible plate, already-enrolled plate, or state outside Illinois — which would matter for an agent handling a real request.

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 schema already documents plate, state, last_name and the plan enum with pricing and defaults. The description only restates the plan economics ("Safety Net is $0 to join; Pro is the all-included plan") and says nothing about state or last_name, so it adds little beyond the schema. Baseline 3 is correct here.

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 first sentence gives a specific verb and resource (start Autopilot America for a plate) plus the actual mechanism: checking the plate for new Chicago parking/camera tickets and contesting by mail. This is clearly distinguishable from siblings like should_i_contest and ticket_win_rate, which are advisory rather than enrollment.

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?

"For when someone wants their Chicago tickets handled, fought, contested or watched going forward" states the triggering intent clearly, and the whole description is scoped to Chicago tickets. It stops short of explicitly naming the alternative siblings (e.g. use should_i_contest for advice instead of signing up), so it falls just short of a 5.

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