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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavior beyond that: the catalog-only restriction and the error outcome for unknown app ids. The field enumeration partially duplicates the output schema rather than adding behavior, which keeps this below 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?

Three front-loaded sentences: what it returns, when to use it, and the failure constraint. The long field enumeration is informative for routing but is partly redundant given an output schema exists, making it slightly heavier than necessary.

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?

For a single-parameter read tool with annotations and an output schema, the definition supplies everything an agent needs: identity/disambiguation from the search tool, the usage trigger, and the error condition for out-of-catalog ids. No behavioral question remains open.

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 one parameter and 100% schema coverage, the schema already explains the app id format including the store.steampowered.com/app/<appid>/ pattern, and the description repeats that meaning rather than extending it. Baseline 3 applies since the schema carries the semantic load.

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 opens with a specific verb and resource ('Returns the stored details of one game from the co-op finder's catalog') plus the lookup key (Steam app id), then enumerates the exact fields returned. This makes the tool unambiguously distinct from find_coop_games, which searches rather than retrieves.

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?

It names the sibling tool and the triggering condition explicitly: 'Use it after find_coop_games when the user asks about one of the games it returned.' It also states a hard precondition — only catalog games are valid and other app ids error — which tells the agent when not to call it.

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