List analysable series

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so safety is covered. The description adds meaningful behavioral context beyond that: the list excludes certain richer-shape kinds and explains why (flattening them would answer a question you did not ask), plus it signals the return includes units. The behavior of omission is disclosed, which goes beyond the annotations.

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?

Every sentence earns its place. The first sentence states the core purpose with units. The second gives a precise call-timing directive. The third explains a non-obvious exclusion behavior and routes to siblings. No filler, and the most important usage guidance is front-loaded immediately after the purpose.

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 zero-parameter, read-only enumeration tool with an output schema present, the description covers purpose, timing, exclusions, and sibling routing. The output schema presumably documents the exact fields, so the description doesn't need to repeat return structure. Nothing needed for correct invocation 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?

The tool takes zero parameters, so schema coverage is trivially 100%. The description adds value by explaining what the returned data will contain (series names and units) and which kinds are intentionally missing. While there are no parameters to document, the description compensates by clarifying the semantics of the returned enumeration.

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 states a specific verb and resource: 'List every series the trend / compare / correlate tools accept, with units.' It clearly names the sibling tools that consume this list, which distinguishes it from all the get_* / log_* siblings whose resources it catalogs. An agent can tell exactly what this tool is for.

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 gives explicit usage timing: 'Call this BEFORE guessing a series name.' It also explicitly names alternatives and exclusion criteria: series with richer shape (sleep stages, workouts, strength sets, food, notes, symptoms, cycle) are deliberately absent and should be read with their own get_* tools. This is clear when-to-use and when-not-to-use guidance.

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