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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds non-obvious behavioral context beyond that: the upstream returns a default mapping for any slug, so the response does not prove the game exists and an unknown-but-valid slug is not an error. This usefully prevents a false inference, though it says nothing about malformed-slug error behavior.

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 tight sentences, front-loaded with the purpose and return shape, followed by the discovery-surface framing and the slug caveat. No sentence is redundant, and the caveat is placed where it matters most for interpretation of results.

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?

An output schema exists, so return values need not be spelled out, and the description still summarizes the key shape (level 1-10 plus Elo band). For a single-parameter read-only lookup, purpose, slug source, and the default-mapping caveat cover everything an agent needs to call it correctly.

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 single `game` parameter is already documented as a required slug from faceit-games, which sets the baseline at 3. The description goes slightly beyond by explaining how the parameter is actually treated upstream (any slug is accepted and a default mapping is returned), which is semantic information the schema does not carry.

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 ("Get FACEIT skill levels and Elo bands for a game") and then describes the exact payload shape: level number 1-10 with an inclusive Elo band. It also positions the tool relative to other data ("the discovery surface for the skill levels that ranking rows report"), so an agent can distinguish it from faceit_games or faceit_player_rank 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 a clear usage context: call this to interpret the level numbers that ranking rows report. It adds a concrete caveat about when the result is meaningful (an unknown-but-valid slug still returns a default). It stops short of naming an explicit alternative or stating a when-not-to-use condition, which keeps it out of the top band.

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