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

Annotations already declare readOnly/idempotent/non-destructive, so the safety bar is met. The description then adds genuinely non-obvious behavior: a $0.001 USDC charge per successful call via x402 on Solana, plus an equivalent HTTPS endpoint — information an agent needs before invoking and that is unavailable anywhere else.

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 examples, then range, then payment/endpoint details — a sensible order. Sentences are short and largely earn their place, though the three-part example block is slightly more illustrative than strictly necessary.

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?

With no output schema and no annotations covering return values, the description should say what a call yields (boolean, step count, full chain). It instead describes the underlying math and the pricing model, leaving the response shape undefined for a tool whose whole purpose is to compute something.

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 0%, so the description must compensate, and it partly does: it restates the valid domain (0 to 999999999999999) in prose and illustrates semantics with concrete values (1 is already happy, 7 takes 5 steps, 4 is unhappy). It still doesn't say whether n is interpreted as decimal digits, what happens at 0, or how the examples map to output, leaving gaps for a single required parameter.

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 defines the happy-number map precisely and gives worked examples (7 reaches 1 in 5 steps, 4 is unhappy), so the domain is unmistakable and no sibling covers happy numbers. However, it never states the operation the tool performs on n — whether it returns a boolean, a step count, or the trajectory — so the actual result is left to inference.

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 statement of when to call this versus the numerous sibling sequence/number-property tools (e.g. digital_root, multiplicative_persistence, collatz_*), nor any exclusions or preconditions. The only usage-adjacent content is pricing and an alternate HTTPS endpoint, which tells the agent how to pay, not when the tool is appropriate.

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