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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds genuinely new context: paid invocation at $0.001 USDC per successful call via x402 on Solana, plus an equivalent HTTPS endpoint. That payment and channel detail is exactly the kind of behavioral fact structured fields don't carry.

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 definition is front-loaded, followed by worked examples, then domain, then commercial/endpoint details — a logical order with little waste. The pricing and URL sentence is dense but earns its place by telling the caller how the tool is paid for and reached.

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 pure function with no output schema, the description is nearly complete: it defines the computation, gives three sample values that pin the output, and covers domain, cost, and transport. Only the absence of any note on return format beyond examples keeps it from a 5.

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% for the single parameter, so the description must compensate, and it does: 'n runs from 1 to 5000' states the domain and the formula makes clear n is the bound of the summation square. It matches the schema bounds without adding new constraints, so not a 5.

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 gives a precise mathematical definition (sum of gcd(x,y) over the square 1<=x,y<=n) with concrete sample outputs (1, 37, 189), so an agent knows exactly what is computed. It does not explicitly disambiguate from sibling gcd-family tools (domb_gcd, franel_gcd, duffinian_gcd), but the name and formula are specific enough to stand alone.

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 only implied: pass an n and get the sum. There is no when-to-use/when-not guidance and no mention of alternative tools for related gcd computations among the many siblings. The pricing and alternate HTTPS endpoint add practical framing but not selection guidance.

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