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

With no annotations, the description carries the full burden. It does disclose real behavior beyond the name: the zero-based indexing convention and the -1 result for zero. However, it says nothing about behavior for negative values, whether the string input is decimal/hex/big-int, or the result type/format.

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 substantive content is a single front-loaded sentence with zero waste, and the edge case is stated inline. The appended '5 free trial calls per signed wallet' promo is boilerplate that doesn't help an agent select or call the tool.

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 one-parameter, no-output-schema utility, the description covers what the tool computes and what it returns including the degenerate case. The remaining gap is input encoding/format, which the sparse schema does not supply either.

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 0% and the single parameter ('value') is typed only as a string. The description clarifies that the parameter is the integer whose top set bit index is returned, and implicitly that it must be integer-valued, which is genuine added meaning. It still omits the string encoding (decimal? hex?) and negative-number handling.

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 precise verb+resource ('Returns the zero-based index of the highest set bit') and pins down the exact return semantics, including the -1 sentinel for zero. This distinguishes it cleanly from the sibling x402-lowest-bit and from related bit tools like x402-bit-length and x402-bit-count.

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?

There is no when-to-use guidance, no prerequisites, and no mention of the closest alternative (x402-lowest-bit, x402-bit-length). Usage is only inferable from the name and the sentence itself.

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