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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds genuinely useful context beyond them: the exact returned fields, the meaning of staleness/manual-entry/paused flags, and an attribution obligation ('repeat each figure's notice when you use it'). It does not cover error behavior for unknown series ids or any rate limits, which keeps it below 5.

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 purpose is front-loaded, but the first sentence is a long comma-run enumeration of return fields, and the closing 'Facts, not investment or other advice' is boilerplate disclaimer rather than operational guidance. The coverage-label example and the notice-repetition rule do earn their place, so it is dense-but-bloated rather than wasteful throughout.

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?

With no output schema, the description correctly carries the return-value burden by listing the fields delivered (value, period, unit, coverage, source, notice, retrieval date, flags). The main omission is failure behavior — what is returned when a series id is unknown or a series is paused entirely — which matters for a single-parameter lookup 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?

There is a single required parameter with full schema coverage, including an example id and a pointer to search_series. The description adds nothing about series_id format or provenance, so the baseline of 3 for high-coverage schemas applies.

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 resource and scope: 'the newest stored value of one series,' which distinguishes it from series_history (multi-point) and search_series (discovery) without naming them. The verb 'retrieve/latest value' is clear, though the description never explicitly contrasts itself with 'series_history' by name, leaving that inference to the agent.

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?

Usage is implied by 'one series' and by the parameter schema pointing at search_series for id discovery, but there is no explicit 'use this when you need a single point-in-time figure; use series_history for a range.' The added guidance is about handling results (read the coverage line, repeat the notice), not about tool selection.

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