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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so safety needs no restatement. The description adds genuinely non-obvious context beyond that: per-call pricing tiers tied to the days window and payment rails (x402 on Base/Solana), plus a hint about the returned array's ordering.

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 core behavior, then a scannable example block, then the pricing note. The bullet list is long but every bullet is a distinct series mapping; the pricing sentence is necessary because cost varies by parameter.

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, the description must carry return-value burden; it only partially does ("most recent observation in the returned array is the current value"). It omits that values are percentage points for rate series but index levels for CPIAUCSL/GDP, and says nothing about how many observations the window yields or error behavior for stale series.

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 coverage is 100% with enums, so the baseline is 3; the description earns above baseline by translating opaque series IDs into real-world meaning (MORTGAGE30US = 30-yr mortgage rate, CPIAUCSL = inflation) and by restating that days=30 maps to the cheapest current-value tier.

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?

States a specific verb and resource ("Returns recent observations for any supported FRED data series") and lists concrete domains (mortgage rates, Treasury yields, CPI, SOFR, GDP). It is distinguishable from bundle/aggregate siblings, but it never names overlapping siblings like get_current_value or get_value_by_date, so the boundary is left implicit.

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?

Gives five concrete use cases with exact series_id and days values, which is unusually actionable when-to-use guidance. It offers no when-not-to-use guidance or explicit routing to the simpler sibling tools (get_current_value, get_value_by_date) that appear to overlap.

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