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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context beyond annotations: it specifies the output format (hex and base64), states that invalid symbols are rejected, and discloses the pay-per-call x402 payment requirement. This is useful behavioral information that annotations do not provide.

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?

Two sentences with no wasted words. The core action and output format are front-loaded, followed by the rejection behavior and payment model. Every clause earns its place.

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 simple decode tool with read-only, idempotent annotations and a single required parameter, the description is nearly complete. It covers the input format, output format, error behavior, and payment requirement. The only minor gap is that it doesn't explicitly describe the response structure, but there is no output schema and the description already states the return format (hex and base64). This is adequate for the tool's complexity.

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 50%: the 'input' parameter has no description in the schema, while '_payment' has a description. The tool description clarifies that 'input' is a Bitcoin/Solana string to be decoded, which adds meaning beyond the bare schema type. However, it does not explain the '_payment' parameter's behavior in detail (e.g., that omitting it returns payment requirements), though the schema already covers that. The description partially compensates for the undocumented 'input' parameter, so a 3 is appropriate.

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 ('Base58-decode'), a specific resource ('a Bitcoin/Solana string'), and the output format ('raw bytes, returned as hex and base64'). It also distinguishes itself from siblings like decode_base64, decode_hex, and decode_url by naming the encoding scheme. An agent can tell this apart from the other decode tools 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?

The description implies usage context by naming Bitcoin/Solana strings and noting it rejects invalid symbols, but it does not explicitly state when to use this tool versus alternatives like decode_base64 or encode_base58. There is no explicit when/when-not guidance or mention of sibling tools. The context is clear enough for a straightforward decode operation, but exclusions are absent.

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