Series this key holds

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

Annotations already cover read-only, idempotent, open-world and non-destructive behavior, so the description adds genuine value beyond them: it discloses the TILLA_API_KEY auth requirement, that the no-argument call returns counts rather than names, and that the returned names are intended inputs to downstream calls. Return shape detail is described only loosely.

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?

Three short, front-loaded sentences organized by mode (no-arg, filtered, prerequisite) with no filler. The colon-heavy telegraphic style is compact but costs a little readability.

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-required-param read tool with annotations and no output schema, the description covers what is returned (lanes per layer with series counts, or series names per layer/lane), the auth prerequisite, and downstream usage. Only the precise response structure is left implicit, which is a minor gap given the tool's simplicity.

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 description coverage is 0% and neither parameter has an enum, so the description carries the full burden — and it does supply the layer vocabulary (raw|derived|node) and the lane vocabulary (1min|hour|daily|...). It leaves the interaction between the two optional parameters (e.g., lane without layer) unstated, so it is not fully compensatory.

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 concrete resource — the inventory of series names available to the caller's API key — and distinguishes unfiltered mode (all lanes per layer with counts) from filtered mode (layer/lane selection listing series names). It is specific about what is enumerated, though the telegraphic phrasing makes the core verb ('lists series') implicit rather than stated outright.

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?

It gives explicit sequencing guidance — 'Call this before tilla_latest / tilla_window and use the names it returns' — which routes the agent correctly against two named siblings. It does not state when not to use it or what happens if names are already known, so it falls short of a 5.

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