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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, covering the safety profile. The description adds valuable behavioral context beyond annotations: it returns only the most recent value (not a time series) and is cheaper than get_series ($0.01 vs $0.05). This provides practical operational detail without contradicting annotations.

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 concise and front-loaded. The first sentence states the core function, and the remaining sentences provide cost, usage context, and alternative tool guidance. Every sentence earns its place with no fluff or redundancy.

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 the tool's simplicity (one parameter, output schema present) and strong annotations, the description fully covers the needed context: what it returns, when to use it, when not to, and the cost trade-off. The alternative tool is named, and the output schema obviates the need to describe return structure.

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%: the series_id parameter has a description and an enum list of valid FRED series IDs. The description does not add further semantic details about the parameter, only mentions 'any supported FRED series,' which is already implied by the schema. Since the schema carries the burden, the baseline of 3 is appropriate.

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 clearly states the tool's function with a specific verb+resource: 'Returns only the single most recent value for any supported FRED series.' It explicitly distinguishes from siblings by mentioning 'single most recent value' and naming the alternative get_series for historical data.

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?

The description provides explicit usage guidance: 'Use this when you need just the latest reading — e.g. current CPI, unemployment rate, mortgage rate' and 'Use get_series instead when you need historical observations.' It also includes the cost advantage, making the when-to-use decision even clearer.

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