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

Annotations declare readOnlyHint=true on a 'put', which would otherwise look contradictory; the description resolves this by explaining the tool returns the exact paid x402 request body for the caller to POST, so no write happens here. It also discloses the $0.001 price, the 8 KB value cap, the endpoint, and that bad input is refused before any charge.

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?

The usage trigger is front-loaded and each clause carries information (storage scope, size cap, price, endpoint, no-charge-on-error). It is dense and multi-clause, but no sentence is filler.

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 compensates by stating exactly what is returned (the paid x402 request plus response schema and example) and how to complete the call. Nothing needed to invoke it 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 description coverage is 100%, so key, value, and ttl are already fully documented with pattern, bounds, and default. The description only restates the 8 KB value cap and adds no TTL or key-format detail beyond the schema, so 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?

The description states a specific verb and resource ('store value ... under key in a private namespace keyed to the wallet that pays') and scopes it as agent memory between runs. This clearly separates it from the kv_get and kv_list siblings, which read the same namespace.

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?

'Use when an agent needs memory between runs without an account' gives an explicit triggering condition, and the payment flow tells the agent exactly when this tool is and isn't the final step (it returns a request body to POST, not the data). It does not name kv_get/kv_list as alternatives or state when not to use it, so it falls 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.