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

Annotations already declare readOnlyHint=true, so the safety profile is covered, but the description adds real value by enumerating the returned tournament state: registration status/window, entrants and survivors, rounds with threads, posted pairs, and signed closed-round results. The note that it never reveals which claim is broken is a useful behavioral constraint.

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?

A single dense sentence, but it is front-loaded with the scope constraint and each clause names a distinct piece of returned data with no filler. Slightly long as one sentence, though 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 carries the burden of explaining the return value, and it does so comprehensively across registration, entrants, rounds, pairs, and results. For a read-only one-parameter tool, an agent has everything needed to call and interpret it.

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?

With a single parameter at 100% schema description coverage ('Lab slug, as returned by list_labs'), the schema already carries the meaning. The description adds no syntax, format, or sourcing detail beyond it, so the baseline of 3 applies.

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?

States a specific verb and resource ('Returns the current tournament') and immediately scopes it with 'Arena labs only (ADR-0040)', which separates it from generic getters like list_labs or get_lab_rules. An agent can tell what it retrieves without opening the schema.

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 'Arena labs only (ADR-0040)' clause gives a precondition that implies when it applies, but there is no explicit when-to-use guidance, no named alternative, and no exclusion criteria. Usage is inferable rather than stated.

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