Find a player's rarest unlocked achievements for any game, ranked by global unlock percentage. See which accomplishments are most uncommon among all players.
Show a player's RAREST unlocked achievements in a game (by global unlock %).
| Name | Required | Description | Default |
|---|---|---|---|
| params | Yes |
Changes observed during successful MCP inspections.
v1.18.0Input schema / $defs / RarestUnlocksInput / properties / appid / titleRemoved value: -"Appid"Input schema / $defs / RarestUnlocksInput / properties / language / titleRemoved value: -"Language"Input schema / $defs / RarestUnlocksInput / properties / limit / titleRemoved value: -"Limit"Input schema / $defs / RarestUnlocksInput / properties / response_format / $refRemoved value: -"#/$defs/ResponseFormat"Input schema / $defs / RarestUnlocksInput / properties / response_format / enumAdded value: +[
+ "markdown",
+ "json"
+]Input schema / $defs / RarestUnlocksInput / properties / response_format / typeAdded value: +"string"Input schema / $defs / RarestUnlocksInput / properties / steamid / defaultRemoved value: -nullInput schema / $defs / RarestUnlocksInput / properties / steamid / titleRemoved value: -"Steamid"Input schema / $defs / RarestUnlocksInput / titleRemoved value: -"RarestUnlocksInput"Input schema / $defs / ResponseFormatRemoved value: -{
- "description": "Output format for tool responses.",
- "enum": [
- "markdown",
- "json"
- ],
- "title": "ResponseFormat",
- "type": "string"
-}Input schema / titleRemoved value: -"steam_get_rarest_unlocksArguments"Output schema / (root)Previous value: -{
- "properties": {
- "result": {
- "title": "Result",
- "type": "string"
- }
- },
- "required": [
- "result"
- ],
- "title": "steam_get_rarest_unlocksOutput",
- "type": "object"
-}New value: +nullv1.14.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The readOnlyHint annotation already establishes that this is a safe read operation. The description adds the ranking criterion ('by global unlock %') which is a useful behavioral detail, but does not disclose return format, pagination, or error behavior. With annotations covering safety, the description adds minimal extra context beyond the core purpose.
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?
A single sentence that is front-loaded with the core purpose and the key differentiator ('by global unlock %'). Zero filler; every word earns its place.
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?
The tool has moderate complexity (5 params, all optional except appid) and no output schema. The description is sufficient to understand what the tool returns conceptually (a list of achievements), but does not hint at the response format, sorting order beyond rarity, or how to use the response_format parameter. Given the annotations and schema richness, the description is adequate but not comprehensive.
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?
The input schema already provides detailed descriptions for all five parameters (appid, limit, steamid, language, response_format). The description does not add any parameter-specific meaning, but since schema coverage is complete, the baseline of 3 applies. The description's mention of 'by global unlock %' indirectly clarifies the sorting logic that affects the limit parameter, but this is not explicitly tied to the parameter.
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 states a specific verb ('Show'), a specific resource ('player's RAREST unlocked achievements in a game'), and the ranking criterion ('by global unlock %'). It clearly distinguishes from siblings like steam_get_player_achievements (all achievements) and steam_get_global_achievement_percentages (global percentages only) by emphasizing rarity and player-specificity.
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 description implies when to use this tool (when you need the rarest unlocks for a player) but does not explicitly name alternatives or state exclusions. It lacks the explicit routing to sibling tools that would make usage guidance strong.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.