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

Annotations already declare read-only, idempotent, non-destructive, open-world behavior, so safety is covered. The description adds genuinely new operational facts: a $0.40 USDC charge per call via x402 on Base or Solana, and that MBS spread and the trend signal are derived rather than raw fields. It omits data freshness/cadence and what happens on payment failure.

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?

Two sentences, front-loaded with the payload inventory and followed by the price. Each enumerated field earns its place because there is no output schema to carry them. The trailing 'Use this for mortgage market analysis' is largely redundant with the field list.

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 input parameters and no output schema, the description carries the return-value burden and does so by listing every field. Combined with the annotation-covered safety profile and the disclosed price, an agent has nearly everything needed; only freshness/units and the type of the trend signal are missing.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The description correctly implies a parameterless call by describing a fixed snapshot rather than a configurable query.

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?

A specific verb ('Returns') plus an enumerated resource: 30yr/15yr rates, 10Y Treasury, Fed funds, MSPUS, HOUST, MBS spread, and a 30-day trend signal. The field-level inventory makes it distinguishable from generic siblings like get_series or get_yield_curve. It stops short of 5 because near-identical bundles (get_bundle_rate_environment, get_bundle_refi_signal) are never named as different.

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?

'Use this for mortgage market analysis' gives a usage context but no when-not-to-use condition and no named alternative. With roughly a dozen sibling bundle and single-indicator tools, an agent must infer which of get_bundle_rate_environment, get_bundle_refi_signal, or get_bundle_macro to pick instead.

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