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TypeScript
Remote

Get Group Members

horizon_get_group_members
Read-onlyIdempotent

Reads a page of group members for a signed-in player to populate group screens or reconcile uncertain membership actions, returning revision and pagination details.

Instructions

Reads group members using a matching player session. Use when: opening a group screen or reconciling an uncertain action. Not for: unbounded group search, automatic pagination or using stale snapshots after a session change. Requires: userId and the player's session: sign in with horizon_signin_email or horizon_signin_anonymous and pass its accessToken as sessionToken. Group membership. Side effects: None (read only). Returns: {groupId,revision,members,nextAfterUserId,serverTime}; one requested page under current memberPageSize. A changed revision between pages requires explicit reconciliation. 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
limitNoExplicit page size no larger than current memberPageSize; default1 stays valid after a reduction. Never automatically follow pages
userIdYesSigned-in player matching the Bearer session
groupIdYesExact group UUID in the current project; never an authorization credential
afterUserIdNoLast user UUID from the preceding member page
sessionTokenYesPlayer accessToken, sent only in Authorization

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 declare read-only, idempotent, non-destructive behavior, and the description adds substantial context beyond that: no side effects, page-size constraints, revision-conflict handling, 401/403/429 semantics, and rollback behavior for related pending actions. It does not contradict the annotations.

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?

The description is long but well structured with labels like "Use when", "Not for", "Requires", "Returns", and "Errors", and the core purpose is front-loaded. Some error and auth details are repeated, but most sentences add operational value for a complex authenticated paginated read.

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?

There is no output schema, so the description carries return-value documentation and does so explicitly: groupId, revision, members, nextAfterUserId, and serverTime. It also covers pagination, revision conflicts, auth failures, and rate limits, making it complete enough for correct invocation.

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 schema already documents the parameters. The description adds useful meaning for authentication semantics: userId must match the signed-in player, sessionToken is the accessToken from a sign-in tool, and limit must not exceed current memberPageSize.

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?

The description states a specific verb and resource: "Reads group members using a matching player session." It also distinguishes scope with explicit exclusions for unbounded group search, automatic pagination, and stale snapshots, so an agent can tell this apart from broader group-reading or reconciliation tools.

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?

It gives explicit "Use when" and "Not for" guidance, and names alternatives such as horizon_get_groups and horizon_get_group_pending for reconciliation. It also explains the required sign-in flow and session-token dependency, 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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