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

Annotations already declare readOnlyHint/idempotentHint/non-destructive, so the bar is lower, and the description still adds real operational context: a free tier of 10 calls/day, a $0.001/call charge afterwards, and the two accepted payment channels (MCP params._meta["x402/payment"] or X-API-Key credits). It also documents the base range and two's complement bit widths. It stops short of describing error behavior for out-of-range bases or invalid digits.

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?

One dense front-loaded sentence carries the conversion semantics before the pricing tail, and nothing is padded. The parenthetical stacking (prefixes, payment paths, served-by host) makes it slightly crowded but each element is functional.

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 single-value converter with full schema coverage, an output schema, and complete annotations, the definition covers semantics, precision constraints, and cost/auth. What remains unstated — invalid-input behavior and return shape — is either conventional or handled by the output schema.

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 a 3 would be the baseline; the description earns above that by supplying a constraint the schema omits — that two's complement applies only for 8-256 bits — which gives the `bits` parameter a valid domain. The 2-36 base range and prefix auto-detection largely restate what `from`/`to`/`value` already say.

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 a specific verb and resource ('Convert big integers between bases 2-36') plus the scope qualifiers that define it: hex/bin/oct/dec, 0x/0b/0o prefixes, and two's complement widths. This clearly separates it from sibling converters such as color_convert or currency_convert without the agent needing to open any 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 never says when to reach for this tool instead of an alternative, nor any when-not condition. The pricing and payment sentence describes cost mechanics rather than usage guidance, so the agent must infer applicability from the purpose sentence alone.

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