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

Annotations already cover safety (readOnly, idempotent, non-destructive, openWorld), but the description goes substantially beyond them: it discloses the output representation threshold ('Past 15 digits the value is a decimal string'), the error condition ('zero is rejected'), and crucially the payment model ('$0.001 USDC per successful call (x402, Solana)') plus an alternate HTTPS endpoint. Cost and auth context are exactly the value-add this dimension rewards.

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?

Front-loaded with the definition, followed by constraints, output format, and payment/endpoint details in a compact sequence. Every sentence is relevant; the density is high but appropriate, with no filler.

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 2-parameter computation tool with no output schema and annotations covering safety, the description is nearly complete: it explains the recurrence, argument bounds, error case, result format threshold, and cost. Minor gaps (return behavior when a modulus is applied, exact boundary at 15 digits) keep it from 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 description coverage is 0%, so the description must carry parameter meaning, and it mostly does: it defines n's range (0–8192), explains that mod optionally reduces the term, and clarifies that a zero modulus is rejected. It leaves the mod parameter's digit-string nature and 600-digit size unexplained, but the core semantics are compensated for.

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 specific verb and resource — 'The nth Jacobsthal number' — and even supplies the recurrence J0=0, J1=1, Jn = Jn-1 + 2*Jn-2, so the agent knows exactly what value is returned. It does not, however, name or differentiate itself from the obvious siblings (jacobsthal_add, jacobsthal_lucas, jacobsthal_power, jacobsthal_sum), which keeps it short of a 5.

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: the tool computes a single term, and the description gives constraints (n in 0–8192, zero rejected, optional modulus) plus pricing. There is no explicit 'use this instead of X' routing among the many jacobsthal_* siblings, so an agent must infer when this is the right call.

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