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horizOn MCP Server

horizOn MCP Server

Official
by ProjectMakersDE
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

Load Cloud Data

horizon_load_cloud_data
Read-onlyIdempotent

Loads a player's cloud save at game start or device switch so saved progress is restored; read-only and requires userId and sessionToken.

Instructions

Reads a player's save game that was stored with horizon_save_cloud_data. Use when: the game starts or the player switches devices and needs the saved progress. Not for: writing (use horizon_save_cloud_data) or balances of server-owned values (use horizon_get_state). Requires: userId and the player's session: sign in with horizon_signin_email or horizon_signin_anonymous and pass its accessToken as sessionToken. Side effects: None (read only). Returns: {found, saveData, revision}. found false with saveData null means the player never saved: this is normal on first start, so initialize default data. revision is the save's server revision (0 = empty slot, 1 after the first save): pass it as expectedRevision to horizon_save_cloud_data. revision null means the server sent none (unknown state, for example a self-hosted simpleServer), not an empty slot. Errors: 401 means the session is missing or expired: sign in again and retry with the new accessToken. 403 for a session means the token belongs to another user: pass the userId that signed in. Needs HORIZON_API_KEY. Every failure returns an error result (isError) with the HTTP status and body: a 401 that horizon_test_connection also returns means HORIZON_API_KEY is wrong, 429 means the account's per-minute rate limit was reached (wait a minute, then retry).

Input Schema

NameRequiredDescriptionDefault
userIdYesPlayer user ID (UUID) from horizon_signup_* or horizon_signin_*
sessionTokenYesaccessToken from horizon_signin_email or horizon_signin_anonymous for this userId; sent as a Bearer session

Output Schema

NameRequiredDescriptionDefault
foundNo
revisionNo
saveDataNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.9.1
    • addedOutput schema / properties / revision
      Added value: +{
+  "anyOf": [
+    {
+      "description": "Server revision (0 = empty slot), to pass as expectedRevision when saving. Null when unknown",
+      "type": "number"
+    },
+    {
+      "type": "null"
+    }
+  ]
+}
  2. Changed3 schema fields changedv1.6.0
    • changedInput schema / properties / sessionToken / description
      Previous value: -"accessToken returned by horizon_signin_email or horizon_signin_anonymous for this user; sent as a Bearer session"New value: +"accessToken from horizon_signin_email or horizon_signin_anonymous for this userId; sent as a Bearer session"
    • changedInput schema / properties / userId / description
      Previous value: -"User ID (UUID) returned by a horizon_signup_* or horizon_signin_* tool"New value: +"Player user ID (UUID) from horizon_signup_* or horizon_signin_*"
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": {},
+  "properties": {
+    "found": {
+      "anyOf": [
+        {
+          "description": "false when the player never saved",
+          "type": "boolean"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "saveData": {
+      "anyOf": [
+        {
+          "description": "The stored save string, null when found is false",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    }
+  },
+  "type": "object"
+}
  3. Changed3 schema fields changedv1.5.5
    • addedInput schema / properties / sessionToken
      Added value: +{
+  "description": "accessToken returned by horizon_signin_email or horizon_signin_anonymous for this user; sent as a Bearer session",
+  "maxLength": 256,
+  "minLength": 1,
+  "type": "string"
+}
    • changedInput schema / properties / userId / description
      Previous value: -"User ID (UUID)"New value: +"User ID (UUID) returned by a horizon_signup_* or horizon_signin_* tool"
    • changedInput schema / required
      Previous value: -[
-  "userId"
-]New value: +[
+  "userId",
+  "sessionToken"
+]
  4. First observedv1.5.4

TDQS

A4.9/5.0
Behavior5/5

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

Annotations already declare read-only/idempotent/no-destruction, and the description goes well beyond them: prerequisite auth chain (sign in, pass accessToken as sessionToken), required HORIZON_API_KEY, and a concrete error taxonomy (401 re-sign-in, 403 user mismatch, 429 per-minute rate limit with retry advice). The only minor redundancy is 'Side effects: None (read only)', which restates readOnlyHint.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Labeled, front-loaded sections (Use when / Not for / Requires / Side effects / Returns / Errors) make it scannable, and the precondition and routing information precede the detailed return and error semantics. Density is high with essentially no filler sentences.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Although an output schema exists, the description supplies interpretation the schema cannot: found=false with null saveData is a normal first-start case requiring default init, revision 0 vs 1 vs null are distinguished, and revision is linked forward to expectedRevision on save. Auth, error, and state-machine context are all present for a two-parameter read.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

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 real semantic constraints the schema cannot: sessionToken must be the accessToken issued for the same userId, and a 403 indicates the token belongs to a different user. It does not describe token lifetime or refresh beyond the 401 retry path.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Reads a player's save game') and ties it to the sibling that produced the data ('stored with horizon_save_cloud_data'). An agent can distinguish this read path from horizon_save_cloud_data and horizon_get_state 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.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit 'Use when' triggers (game start, device switch) and explicit 'Not for' exclusions that name the correct alternatives (horizon_save_cloud_data for writes, horizon_get_state for server-owned balances). Both directions of routing are covered.

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

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