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horizOn MCP Server

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by ProjectMakersDE
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TypeScript
Remote

Update Group

horizon_update_group
DestructiveIdempotent

Replaces a group's metadata, private data and join mode after the player confirms the settings, using the current revision to detect conflicts so writes are not repeated blindly.

Instructions

Replaces the complete group metadata and private JSON object. Use when: the player explicitly confirms the group settings. Not for: choosing/reusing a group ID or resending uncertain writes with a new revision. Requires: userId and the player's session: sign in with horizon_signin_email or horizon_signin_anonymous and pass its accessToken as sessionToken. Leader/officer and the current group revision. Side effects: Changes metadata, private data and join mode. Existing pending requests remain. Returns: {groups:MyGroupsView,group:GroupView|null}. groups is the actor's complete snapshot, never the target's private state. group is null after leave/delete; nonmembers never receive private data. Replace only the matching host/project/player cache. Errors: Use horizon_get_groups and horizon_get_group_pending to reconcile state. 409 REVISION_CONFLICT or uncertain response: read and reconcile intent, never refresh the revision and repeat automatically. Pending decisions require the original requestId; REQUEST_NOT_FOUND means it was removed/replaced. INBOX_FULL rolls back the entire action. 403 rejects group role, session or bilateral block violations. 429 is reported without automatic retry. 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
dataYesRequired finite JSON object; current maxDataBytes/maxDataDepth are server policies. Client JSON bytes can differ from stored dataJson after number normalization; the server validates the complete stored representation. No default2048-byte/depth16 clamp. Only members/admins can read it.
nameYesNonblank display name under current maxNameBytes; server enforces the complete BSON envelope
userIdYesSigned-in player matching the Bearer session
groupIdYesExact group UUID in the current project; never an authorization credential
joinModeYesWhether players join directly, request admission or need an invitation
descriptionYesPublic description under current maxDescriptionBytes
sessionTokenYesPlayer accessToken, sent only in Authorization
expectedRevisionYesExact reviewed revision; never replace automatically after an uncertain response

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv1.9.1

TDQS

A4.8/5.0
Behavior5/5

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

Annotations already flag destructive/idempotent/openWorld, but the description adds material context beyond them: it names what changes (metadata, private data, join mode), notes that pending requests survive, documents the return shape and cache-scoping rule, and explains revision/409, INBOX_FULL rollback, 403/429/401 semantics. This is rich behavioral disclosure that a destructive mutation genuinely needs.

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

Conciseness4/5

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

Front-loaded with the verb+scope, then labeled Use when / Not for / Requires / Side effects / Returns / Errors sections, which is good structure. It is long and has minor redundancy (429 and 401 are each revisited in the final sentence), so it earns most but not every sentence.

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?

With 8 required params, a nested JSON object, and no output schema, the description carries the burden and does: it describes return values ({groups, group|null}), private-state leakage rules, side effects, auth flow, and error reconciliation. An agent could call and recover correctly from this text alone.

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 acquisition semantics not in the schema: userId plus a sessionToken obtained from horizon_signin_email/anonymous, plus the leader/officer role requirement and the 'never refresh the revision and repeat automatically' rule for expectedRevision. Meaningful beyond the property descriptions, though it doesn't add much per-field detail.

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 precise verb+resource+scope: replaces the *complete* group metadata and private JSON object. That full-replacement framing is reinforced by a 'Not for: choosing/reusing a group ID' exclusion, which separates it from horizon_create_group and other group tools without requiring the schema to be opened.

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 when/when-not: 'Use when: the player explicitly confirms the group settings' and 'Not for: choosing/reusing a group ID or resending uncertain writes with a new revision.' It also routes error recovery to horizon_get_groups and horizon_get_group_pending, giving the agent concrete alternatives rather than leaving inference to it.

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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