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

Annotations already cover readOnly/idempotent/openWorld, but the description adds real behavioral detail beyond them: unknown key returns `present:false`, lineup is capped at ≤25 acts, names are display-only `untrusted_text`, and auth is linked. The telegraphic phrasing ("Credit attribution.line", "Auth: linked") is terse enough that an agent may not fully decode it, keeping it from a 5.

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 six short labeled lines (purpose, use, inputs, returns, caveats, auth) with no filler and the identification facts front-loaded. The compressed fragment style costs a little readability but nothing is wasted.

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 usefully enumerates the returned fields (`display`, `slug`, `id`, `data.identity`, `data.lineup`) and the not-found shape, which an agent needs. Missing finer details such as what `attribution.line` actually contains or pagination behavior beyond the 25-act cap.

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 the schema's `key` description already explains the slug/no-index situation, so the description's "Inputs: `key`: the festival slug" largely repeats it. It reinforces the ask-the-user guidance but adds no new syntax or format meaning beyond the schema — the baseline 3 for high coverage.

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 names a specific resource (a festival card) and enumerates its contents — header facts, identity, lineup, acts linked to artist cards where a cluster_id exists — which clearly distinguishes it from get_artist/get_label/get_release. The opening is a noun phrase rather than a verb, but the substance is unambiguous.

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?

"Use: a festival whose slug you have" gives a clear triggering condition, and "crate publishes no festival index — ask for the key" warns the agent not to look for a discovery path. It also states a precondition (ask first if ambiguity.state is not none). No explicit named alternative among siblings, so not a 5.

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