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

With no annotations, the description carries full disclosure burden. It discloses paid cost ($0.04 via x402), composite nature (combining four calls), and single-key scope. It does not cover error behavior or missing-key handling, but the core behavioral traits are transparent.

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?

Three sentences plus an input hint, all front-loaded with the most important information (cost, composite, use cases). No filler or redundant repetition of schema titles.

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?

Given no output schema and no annotations, the description explains the tool's return substance (latest value, velocity, rank, z-score), usage context, and input expectations. It is slightly incomplete around payment_header behavior and failure modes, but adequate for a single-key composite lookup.

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. It clarifies dataset, key, and numeric field must match dataset naming exactly, which adds meaning. However, it omits the payment_header parameter entirely and does not explain how field is used in ranking or z-score calculation, leaving partial coverage.

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?

Description clearly identifies the tool as 'one-call composite for a single key' returning latest value, velocity, rank, and anomaly z-score. It distinguishes itself from sibling tools like anansi_movers and anansi_data_history with explicit scope.

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?

Provides explicit when-to-use ('when you have one specific key and want a verdict rather than raw series') and when-not-to-use instructions, naming specific alternatives for surveying many keys (anansi_movers) and fetching full series (anansi_data_history).

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