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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds meaningful behavioral context: it returns observations for each series and constrains them to the same date range, which clarifies how the multi-series comparison is structured.

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 concise sentences with no filler. The first sentence states the action, resource, and constraint; the second explains the return shape and provides concrete use cases. Every sentence earns its place.

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 read-only multi-series retrieval tool with complete schema coverage and safety annotations, the description is largely sufficient. It explains the return shape ('observations for each series') and alignment ('same date range'), leaving no critical gap for correct invocation. A fully detailed output schema would push this to 5, but its absence is partly mitigated by the clear return statement.

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 all four parameters are already documented in the schema. The description reinforces the 2-to-5 series constraint and the date-range concept, matching the schema but adding no new parameter-level detail.

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 uses a specific verb ('Compare') with a precise resource ('FRED series'), scope ('side-by-side'), and cardinality ('2 to 5'). It clearly distinguishes itself from single-series siblings like fred_observations by emphasizing multi-series comparison over the same date range.

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 concrete use cases ('ratio analysis', 'cross-series correlation') that make the intended scenario clear. It does not explicitly mention alternatives or when-not-to-use, but the comparison-focused framing sufficiently orients an agent toward this tool over single-series tools.

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