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

Annotations already declare this is a non-read-only, non-idempotent, non-destructive, closed-world mutation, so the safety profile is covered. The description adds only the vague 'synthetic token' note and never says what entering actually does (creates match state? assigns seats? fails if a match is open?), leaving the behavioral picture thin beyond the annotations.

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?

Very short and front-loads the WHEN condition, which is good, but the opening name restatement and an example that merely duplicates the schema consume roughly half the text without adding information.

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 an output schema present and full schema coverage, the description only needs to convey purpose and sibling routing, which it does. The unexplained 'synthetic token' phrase and missing preconditions for opening a match are the only real gaps.

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 100%, so the schema already documents key, role, and opponent. The embedded example echoes the same two required fields without adding format, constraint, or handle-resolution detail, so the baseline 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: 'open a Rogue Colosseum match', and explicitly separates it from arena_join (public Arena games). The leading 'colosseum_enter.' restatement of the name adds nothing, and 'synthetic token' is left unexplained, which keeps it from a 5.

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 'WHEN:' clause gives an explicit trigger and names the alternative (arena_join) with the condition that selects it. It does not address adjacent colosseum siblings like colosseum_defend or colosseum_probe, so the routing is clear but not exhaustive.

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