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

Annotations already declare readOnly, idempotent, non-destructive behavior, so the bar is lower; the description still adds real value by disclosing that a zero modulus is rejected, that results past 15 digits are returned as decimal strings, and that each successful call costs $0.001 USDC. The side-effect-free nature is not restated in the text, but annotations cover that and the remaining behavioral quirks are well surfaced.

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 description is front-loaded with the definition, then constraints, then output-format and pricing/alternate-endpoint notes; every sentence is informative and there is no redundant restatement of the schema.

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, no-output-schema tool, the description covers the recurrence, index bounds, modulus behavior rejection, large-value return format, and cost/transport details—enough for an agent to call it correctly without consulting anything else.

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 does: it explains that n is the zero-based index (with T0/T1=0, T2=1) bounded to 0–4096 and that mod optionally reduces the term but must be nonzero. The string type of mod is left to the schema, but overall the semantics of both parameters are meaningfully supplemented.

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 computation ('The nth Tribonacci number') and defines the sequence recurrence, which clearly separates it from unrelated siblings like tetranacci or trib_sum. However, it never distinguishes itself from close siblings such as trib_index, trib_step, or trib_mod, leaving the agent to infer the boundary.

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: mentioning that 'an optional modulus reduces the term' suggests this tool can replace a separate mod variant, but there is no explicit when-to-use or when-not guidance relative to trib_mod, trib_index, or trib_step.

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