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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds value annotations cannot: the authentication requirement ('Needs TILLA_API_KEY') and the fact that omitting arguments yields an aggregate summary rather than a flat list. It does not discuss pagination or result size limits for large inventories.

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?

Roughly three dense sentences, front-loaded with the tool's identity and then the two parameter modes, with the prerequisite last. The telegraphic style ('No arguments:', 'layer=raw|derived|node') is efficient rather than padded, though the clipped phrasing takes a re-read.

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 must describe returns, and it does: aggregate lane-per-layer counts in the default case, series names in the filtered case. Combined with the auth note and the ordering guidance, an agent has enough to call this correctly; only edge-case behavior (invalid layer/lane, combined filters) is unaddressed.

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%, so the description must carry the load, and it largely does: it defines the default (no arguments) behavior and enumerates the accepted values for layer (raw|derived|node) and lane (1min|hour|daily|...). It does not state whether the two filters can be combined or what happens with an invalid value, so it falls short of full compensation.

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 verb+resource: it enumerates every lane per layer with series counts, or every series name within a given layer/lane. The two modes (no-arg aggregate vs. filtered listing) are spelled out, which no sibling does. The lead sentence 'Exactly what the caller's key holds' is slightly indirect, but the following clauses remove ambiguity.

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 an explicit ordering instruction: 'Call this before tilla_latest / tilla_window and use the names it returns,' naming the two siblings it feeds. That is both a when-to-use rule and the reason the tool exists, leaving nothing to inference.

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