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

With no annotations, the description carries the full burden and does meaningful work: it discloses the payment flow for tier=full ('returns the payment requirements and does not sign or pay') and names return fields for tier=free (source_url, verified_date). It leaves undisclosed what full tier actually returns, how ranking is ordered, and any rate limits.

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 tight sentences, front-loaded with purpose and followed by tier behavior. Every sentence carries information; the audience-default sentence is the only near-redundant one against the schema.

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 7-parameter tool with no output schema, the caller learns the free-tier return shape and the full-tier payment handshake, which are the non-obvious parts. It omits what the ranked result set looks like on tier=full, which would be the remaining gap.

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 restates the audience defaulting rule that the schema already documents and adds only that tier=free yields one plan. It adds nothing about usage bands, budget, models, type, or the limit cap beyond what the schema already says.

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 and resource: 'Rank coding-agent plans from PlanLimits.' That is concrete enough for an agent to know it is a ranked lookup over a plan catalog. It does not, however, differentiate itself from the sibling plan_fit_info, so the agent is left to infer which one to open.

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?

Gives clear conditions for the two modes: tier=free needs no payment and returns one plan, while tier=full requires x402. The exclusion that the server 'does not sign or pay' sets an explicit boundary on what the caller must do next. It stops short of naming when to prefer the sibling plan_fit_info.

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