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horizOn MCP Server

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by ProjectMakersDE
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TypeScript
Remote

Get Marketplace Limits

horizon_get_marketplace_limits
Read-onlyIdempotent

Reads current marketplace limits, capabilities, and configuration for a user session, helping you verify the player's marketplace state before taking explicit actions.

Instructions

Reads current own marketplace state or configured limits. Use when: explicit marketplace actions after reading horizon://docs/marketplace. Not for: automatic trading, price polling or generated replacement operations. Use horizon_get_marketplace_operation to reconcile the original intent. 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: Read only. No automatic refresh or polling. Returns: {limits,capabilities,config,serverTime} Errors: 409 conflicts require explicit reconciliation, never fresh revisions or operation IDs on an unknown outcome. Missing OPERATION_NOT_FOUND does not prove nonexecution. 422 capacity/balance/daily-limit errors preserve atomicity. 429 schedules no retry. Full Inbox returns pending without losing the original item. 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
userIdYesActive player matching the current session and project
sessionTokenYesCurrent accessToken sent only as Bearer

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv1.9.1

TDQS

A4.1/5.0
Behavior5/5

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

Goes well beyond the annotations by disclosing the auth chain (sign in via horizon_signin_email/anonymous, pass accessToken as sessionToken), the HORIZON_API_KEY requirement, the exact return shape {limits,capabilities,config,serverTime}, no-refresh behavior, and how 401/403/429 should be handled. It is consistent with readOnlyHint=true and destructiveHint=false.

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

Conciseness3/5

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

Front-loaded with the when/when-not guidance, which is good. However the Errors block contains a large amount of boilerplate that cannot apply to a read-only limits read (409 conflict reconciliation, 422 capacity/balance/daily-limit atomicity, 'Full Inbox returns pending'), diluting the signal.

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

Completeness4/5

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

For a two-parameter read with full schema coverage and rich annotations, the description supplies everything needed to invoke it correctly: authentication path, return shape, and error handling. The relevance of some error cases is questionable, but nothing essential is missing.

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 already 100% for the two parameters, so the schema carries the basics; the description adds real meaning by explaining that sessionToken is the accessToken from a sign-in call and that the userId must match the signed-in player.

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: reads the caller's own marketplace state / configured limits. It is distinguishable from horizon_get_marketplace and horizon_get_marketplace_rules in broad strokes, though 'marketplace state or configured limits' is slightly blurred and does not explicitly contrast with the sibling 'rules' tool.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

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

Provides explicit 'Use when' and 'Not for' clauses plus a named alternative (horizon_get_marketplace_operation). The alternative routing is somewhat mismatched for a read-only limits call (reconciliation applies to operations), but the when/when-not framing is clear.

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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