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horizOn MCP Server

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Remote

transfer group leadership

horizon_transfer_group_leadership
DestructiveIdempotent

Transfers group leadership to an existing member using a reviewed group revision after explicit player confirmation, requiring a valid session and exact pending request ID.

Instructions

Applies the explicit transfer group leadership action using the reviewed group revision. Use when: the player explicitly confirms this group action. Not for: replacing reviewed revisions/request IDs, bypassing a leader's block, or retrying automatically after uncertainty. Requires: userId and the player's session: sign in with horizon_signin_email or horizon_signin_anonymous and pass its accessToken as sessionToken. Current group revision and the exact pending requestId where applicable. Side effects: Leader transfers leadership to an existing member, becoming an ordinary member. No automatic retry. Same-revision replay cannot create a second effect. 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
userIdYesSigned-in player matching the Bearer session
groupIdYesExact group UUID in the current project; never an authorization credential
sessionTokenYesPlayer accessToken, sent only in Authorization
targetUserIdYesOther player in this project
expectedRevisionYesExact reviewed revision; never replace automatically after an uncertain response

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv1.9.1

TDQS

A4.6/5.0
Behavior5/5

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

Annotations already declare destructive=true and idempotent=true; the description then explains the actual consequence (leader becomes an ordinary member), denies automatic retry, and clarifies that same-revision replay cannot duplicate the effect. It adds auth, rate-limit, and rollback (INBOX_FULL) semantics far beyond the structured hints.

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 purpose, use-when, not-for, requires, side effects, returns, then errors — a logical, skimmable order. It is dense and the error section is long, but for a destructive, multi-error-mode operation most sentences carry real decision value.

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?

Given the absence of an output schema, the description supplies the return shape ({groups, group}), privacy guarantees (actor's snapshot, never target's private state), and a full error taxonomy, so an agent has everything needed to call and recover correctly.

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

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the schema already documents all five parameters, anchoring the baseline at 3. The description adds useful framing (sessionToken is the accessToken; expectedRevision must be the reviewed revision, not auto-refreshed), but also references a pending requestId that does not exist in this schema, creating minor confusion without net semantic gain.

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+resource (transfer group leadership) scoped by the reviewed revision, which distinguishes it from sibling mutations like set_group_member_role or leave_group. An agent can identify the exact operation without opening the 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' (player explicitly confirms) and 'Not for' clauses naming concrete exclusion scenarios (bypassing a block, auto-retry, replacing reviewed revisions). It also points to horizon_get_groups and horizon_get_group_pending for reconciliation, leaving little to inference.

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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