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

Annotations already cover the safety profile (readOnlyHint, openWorldHint), but the description adds genuinely useful context beyond them: pricing ($0.001 per successful call via x402 on eip155:8453), a 5 free calls/day quota across all tools, and the fact that binary decode results are returned as hex.

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, front-loaded with the core operation before the cost/quota note. Dense but every clause carries information an agent needs (mode semantics, hex return, billing).

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?

No output schema exists, so the description carries the return-value burden and does so adequately by specifying hex for binary decode results. Remaining gap is minor: it doesn't mention output shape for the encode direction.

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, but the description adds meaning the schema lacks: the encode input is treated as UTF-8 text, base64url applies to encoding, and binary decode output comes back as hex rather than raw bytes.

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 specific verbs and resource: encode a UTF-8 string or decode base64, including the base64url variant. This clearly separates it from siblings like hash, uuid, and jwt_decode.

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?

Usage is implied by the encode/decode framing, but no explicit guidance is given on when to choose this over siblings such as hash or jwt_decode, and no exclusions or prerequisites are stated.

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