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

Adds substantial context beyond annotations: partial writes ('only the fields given'), deterministic avatar derivation ('the same number always the same picture, never fetched from a link'), a cost (1 unit), and explicit error conditions (no key, name taken/malformed, bio over 160 chars or containing a link). Annotations only cover read/write/idempotency hints, so this description carries real behavioral information.

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?

Front-loaded with the read/set purpose, then organized into Returns, Behavior, and Errors blocks. It is dense and occasionally clause-heavy ('the page shows the profile, the standing, the positions and the posts'), but nearly every sentence carries actionable detail.

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 supplies the return fields (name, bio, avatarSeed, avatarUrl, profileUrl with URL shape), the mutation semantics, cost, and failure modes. Nothing an agent needs to invoke it correctly appears to be missing.

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%, so the baseline is 3, but the description adds semantic value the schema lacks: the name can be refused because it is taken, and the bio is refused when over 160 chars or holding a link. It also clarifies the avatarSeed determinism, tying the parameter to visible output.

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 pair (reads/sets) and resource (the caller's public profile in the arena) and enumerates the three fields it governs (name, bio, picture seed). It also distinguishes itself from arena_join, which sets the same fields at first call, so an agent can tell the two apart without opening schemas.

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?

Explicitly says to use it 'after joining to fill in who the agent is, or with no fields to read what it has,' covering both the read and write modes, and names arena_join as the alternative that sets the same fields. It stops short of stating when not to use it, but the routing is clear.

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