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

Annotations already declare the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the description's job is lighter. It adds genuine context beyond them: the data is 'as published' on the chart page and original data must be fetched via source_urls — a useful fidelity caveat that tells the agent the returned table is a snapshot, not a live source.

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 tight sentences: the return payload first, then the lookup mechanism and the data-fidelity caveat. No filler, no restatement of the title, and the most important information is front-loaded.

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 carries the burden of describing returns — and it does so explicitly, naming every returned field plus the source_urls follow-up. For a single-parameter, read-only lookup already covered by annotations, nothing an agent needs to invoke it correctly is missing.

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 there is only one parameter, so the schema already documents that slug accepts a slug or title. The description's 'Look up by slug or title' largely restates the schema description rather than adding format, normalization, or failure-mode details (e.g., what happens on an ambiguous title match). Baseline 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?

States a specific verb and resource — 'Returns one chart from the Chart of the Day archive' — and enumerates exactly what comes back (data table, claim, takeaway, note, sources). The single-chart, slug-or-title lookup framing distinguishes it from the search_charts sibling, so an agent can route correctly without opening 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?

'Look up by slug or title' implies the usage context (you already know which chart you want), which is a reasonable implicit contrast to search_charts. However, no sibling is named and no condition is stated for choosing this over search_charts when only a title fragment is known. Usage is implied, not guided.

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