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

Beyond the readOnly/idempotent/non-destructive annotations, the description discloses that this returns a paid x402 request rather than the data itself, that the caller must invoke the URL with an x402 or MPP client, and that it costs $0.001 per call with validation before charging. These are exactly the non-obvious traits an agent needs, though absence-of-key behavior is unstated.

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 purpose is front-loaded, but the middle sentences are dense and use 'Returns' twice for two different things (the value vs. the payment request), which reads ambiguously. The schema-link clause is low-value padding relative to the surrounding content.

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 responsibly characterizes the return payload (text, parsed JSON, size) and the two-step paid retrieval flow. The main gap is the not-found / missing-key outcome, which an agent would need to handle 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% and the single key parameter is fully documented with its pattern and length constraints in the schema. The description adds no meaning beyond the schema for the key itself, so the 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 concrete verb and resource: retrieve a value previously stored via /kv/put, returning text, parsed JSON, and size. Naming /kv/put distinguishes it from sibling kv_put/kv_list, though the pivot into x402 payment mechanics dilutes the opening a bit.

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?

The phrase 'Use when an agent needs a value it stored earlier with /kv/put' gives a clear trigger and implicitly excludes keys never written. However, it never mentions kv_list as the alternative for enumerating keys, nor what to do when the key is unknown.

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