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

Goes well beyond the annotations: it explains the idempotent return shape (already:true), per-achievement min_trust with a default of client, and the specific AUTH/SIGN scenarios. These are behavioral facts the annotations (readOnlyHint, openWorldHint, destructiveHint) cannot convey.

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-loads the core action, then layers idempotency, rules, and auth in ordered sentences. Dense but each clause carries a distinct fact; the auth sentence is somewhat packed but still readable.

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 correctly documents the return payload (the achievement, its points, unlocked_at), covers idempotency, auth requirements, and trust rules. Nothing an agent needs to call it correctly is 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 description coverage is 100%, so the schema already documents all five parameters. The description adds the session default ('player's latest session of this game') and references min_trust, but does not otherwise enrich parameter meaning, matching the baseline 3.

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+resource: 'Unlock an achievement of a game for a player.' It also anchors itself against the sibling submit_score ('same proof, trust, session and author rules as submit_score'), letting an agent distinguish the two without opening a 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?

Gives clear usage context: idempotent re-calls return already:true, and it specifies the auth modes (sign as the player, owner session token, or a referee of the game). It lacks explicit when-not or a direct comparison to other game-play tools, but the conditions for correct invocation are well covered.

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