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

Annotations already establish read-only/idempotent/non-destructive, and the description goes well beyond them: default windows (1 year daily, 5 years otherwise), the 500-point cap with a truncation note, error behavior for unknown keys, 60 calls/min per IP rate limit, and once-per-business-day refresh cadence.

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 purpose, then routing, then defaults and limits - a logical order with no filler. It is dense but each clause carries distinct information (defaults, cap, error, rate limit), though the single long block is slightly heavy for a 3-parameter tool.

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?

Covers everything an agent needs before calling: required key provenance, default windows, result cap and truncation signaling, error semantics, rate limits, and auth requirements. With an output schema present, it correctly refrains from enumerating return fields in detail.

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%, so the baseline is 3, but the description adds value the schema lacks: the default behavior when neither from nor range is supplied, and concrete well-known key examples beyond the schema's sample values. It does not restate the from/range precedence rule that the schema already carries.

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 (return) and resource (historical values of one series) plus the metadata set returned. It explicitly distinguishes itself from get_projection ("use get_projection for future ones"), so an agent can route correctly without reading 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?

Gives explicit when-to-use (past/current values), when-to-use-the-alternative (future values -> get_projection), and a prerequisite (a key from search_series). It even supplies well-known keys, which is unusually actionable guidance.

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