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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds one behavioral detail beyond that – results are popularity-ordered – but says nothing about return shape or pagination, which matters since there is no output schema. Modest value-add against an already-annotated tool.

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 tight sentences, with the core purpose front-loaded before the examples and the routing guidance last. The three ID examples are useful but slightly redundant with the schema's own category reference, so it's efficient rather than maximally lean.

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, read-only catalog listing with full schema coverage and no output schema, the description covers purpose, ID semantics, and routing versus search. What's returned (series IDs/titles) and any page-size behavior are left implicit, though the limit default is documented in the schema.

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 100%, so the baseline is 3. The description goes beyond the schema's generic 'See https://fred.stlouisfed.org/categories/' pointer by supplying concrete ID-to-topic mappings (32991 = Interest Rates, 32263 = Money Stock, 9 = National Accounts), which materially helps the agent map intent to a value.

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 names a specific verb (List) and resource (FRED series within a category) and adds scope ('most popular'). It also distinguishes itself from search-based siblings with 'browse FRED structurally rather than via search,' so an agent can route without opening either schema.

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?

It gives a clear selective condition ('browse FRED structurally rather than via search'), which routes the agent away from fred_search. It stops short of naming the sibling tool explicitly or stating when-not to use this tool, so it's clear context without full alternatives coverage.

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