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

With no annotations, the description carries the full behavioral burden and does well: it discloses exact big-integer handling (the key correctness edge case) and the cost/payment model ('$0.005 per call, paid over x402 (USDC)'). It omits error behavior and return shape, but the precision and billing disclosures are genuinely useful context beyond the schema.

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?

Three tight sentences: purpose first, then the motivating use case, then cost. Every sentence earns its place and nothing is redundant.

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 two-parameter converter with no output schema, the description covers purpose, use case, precision behavior, and cost. It could state the return format, but for a transparent value-conversion tool the coverage is nearly sufficient.

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 both 'as' (with its hex|decimal|text modes) and 'value' are already documented in the schema. The description adds purpose framing but no additional parameter syntax or format detail, 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 names a specific verb ('Converts between') and the exact resource set ('hex, decimal and UTF-8 text'), so an agent knows precisely the transformation offered. It does not explicitly differentiate from adjacent utilities like util_base64 or util_units, but the named format set is self-distinguishing.

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?

It gives a concrete use case: 'For reading raw RPC output, which comes back as hex and overflows a JavaScript number.' This tells the agent when the tool is applicable, though it names no exclusions or alternative tools for related conversions.

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