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horizOn MCP Server

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by ProjectMakersDE
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TypeScript
Remote

Block Player

horizon_block_player
DestructiveIdempotent

Blocks a player using the reviewed snapshot revision, atomically removing friendship and both request directions. Requires a signed-in session and current revision to avoid conflicting actions.

Instructions

Blocks Player using the reviewed player revision. Use when: the player explicitly requests this social action. Not for: automatic retries after timeout, automatic acceptance of crossed requests or changing expectedRevision without reconciling intent. Requires: userId and the player's session: sign in with horizon_signin_email or horizon_signin_anonymous and pass its accessToken as sessionToken. A current snapshot revision. Side effects: Adds your block and removes friendship and both request directions atomically. Does not notify the blocked party. No automatic retry. Repeating the same revision cannot create a second effect. Returns: Complete {userId,revision,friendCode,friends,incoming,outgoing,blocked,limits,serverTime} snapshot. Replace the matching host/project/player cache. lastActiveAt is the latest retained login, null when unknown; it is not online presence. Errors: 409 REVISION_CONFLICT or an uncertain response: get a new snapshot and reconcile intent, never silently replace expectedRevision and repeat. 404 FRIEND_REQUEST_NOT_FOUND means this request was removed or replaced; do not act on a newer ID. INBOX_FULL rejects the entire send/accept. Friend/request/block capacity limits reject additions while existing data remains removable. 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 UUID matching the session
sessionTokenYesPlayer accessToken sent only as Authorization Bearer
targetUserIdYesThe other player UUID in the same project
expectedRevisionYesExact revision from the reviewed actor snapshot; never refresh and substitute automatically

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv1.9.1

TDQS

A4.5/5.0
Behavior5/5

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

Goes well beyond the annotations: atomic removal of friendship and both request directions, no notification to the blocked party, no automatic retry, and idempotency keyed to the revision. It also documents auth requirements, cache replacement, and specific error semantics (409, 404, INBOX_FULL, 401, 403, 429), which is exactly the behavioral detail needed for a destructive mutation.

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 core action and organized into labeled sections (Use when, Not for, Requires, Side effects, Returns, Errors), so it is easy to scan. It is dense and long, but most sentences carry operational value for a destructive, idempotent mutation; a few error details could be trimmed without losing meaning.

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?

Even without an output schema, the description specifies the returned snapshot shape and instructs the caller to replace the matching cache. It also covers auth, side effects, idempotency, and error recovery, leaving nothing critical for an agent to infer before invoking the tool.

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 meaning: sessionToken must be the accessToken from horizon_signin_email or horizon_signin_anonymous, and expectedRevision must come from a reviewed snapshot and never be silently replaced. The 409 guidance reinforces how expectedRevision is intended to be used.

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

Purpose4/5

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

States a specific verb and resource ('Blocks Player') and adds scope ('using the reviewed player revision'), so the action is unambiguous. It does not explicitly contrast with the sibling horizon_unblock_player, but the name and description make the distinction clear enough 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?

Explicitly names the triggering condition ('the player explicitly requests this social action') and enumerates exclusions: no automatic retries after timeout, no automatic acceptance of crossed requests, and no silent expectedRevision changes. This is a textbook when/when-not section with no inference required.

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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