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

Annotations already declare readOnlyHint and destructiveHint=false, so the 'reads or computes only and changes nothing' clause is largely redundant. What the description adds beyond annotations is valuable: per-call pricing via x402 USDC or card key, failed calls free, first 25 free, and a 'dated snapshot' rather than live data — all reinforcing the idempotentHint=false that repeat calls cost money.

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?

Coverage and scope are front-loaded, followed by use guidance and then the example. It is a dense single block with a slightly redundant safety clause, but no sentence is filler.

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?

No output schema exists, yet the description specifies what the response contains (per-security averages plus marketable, non-marketable and all interest-bearing totals) and the time horizon. That is sufficient for correct invocation of a two-parameter read tool.

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% and the schema already states months is 1-24 with default 12, so the 'up to 24 months' text and months=12 example mostly restate it. The description does add a little on the security filter by naming values the schema truncates ('non-marketable series', 'floating rate notes', 'all interest-bearing debt'), but no matching syntax is given.

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?

Uses a specific verb-plus-resource framing: 'Average interest rates on US Treasury securities by month', then enumerates the security classes covered (bills, notes, bonds, TIPS, FRNs, non-marketable) and the aggregates. This clearly differentiates it from siblings like econ_national_debt or econ_inflation without the agent needing to open a 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?

'Use for the US government's borrowing cost, a rate trend or macro context; not a live yield curve' gives both a positive use case and an explicit exclusion. It stops short of naming a specific alternative tool for current yield-curve data, so routing to a sibling is still left to inference.

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