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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open world), so the bar is lower. The description still adds real value: an auth requirement ('Needs a key'), the default value of `at` ('the minute just closed'), and the per-lane response shape ('bar, complete, series, values') — useful since no output schema exists.

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 short sentences with no filler; the default-value detail and response shape are packed in efficiently. The leading tagline ('Your whole plan, live') is marketing rather than specification and pushes the substantive scope to second position, which is the only real structural weakness.

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 0% schema coverage, no output schema, and fully custom domain terms ('lane', 'bar', 'complete', 'series'), the description is the sole source of meaning and leaves core concepts undefined. An agent can form a rough idea of the call but cannot confidently construct `lanes` or interpret the returned keys.

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 the schema only offers titles ('At', 'Lanes'). The description compensates for `at` with a format and default, but says nothing about `lanes` — not its syntax (list? comma-separated? glob?), not its filtering behavior, and not what happens when it is null. Half the parameters remain opaque in both schema and description.

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 says it returns 'every series the key holds on every lane that closed at a boundary', which conveys a read of time-bound series data, but the verb is implied ('in one call') and the domain vocabulary ('lane', 'bar', 'series') is never grounded. It does not distinguish itself from close siblings like tilla_latest, tilla_window, or tilla_sample, so an agent cannot tell which of these to pick from the text alone.

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?

'default the minute just closed' implies the intended polling/tick use case and 'Needs a key' flags a prerequisite, so usage is inferable. However, no alternative sibling is named and there is no when-not guidance, so the agent must guess between this and tilla_latest/tilla_window for adjacent needs.

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