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List a User's Fantasy Leagues

fantasy_list_user_leagues
Read-onlyIdempotent

Discover an account's leagues on a provider, mainly WITHOUT a connected profile (a connected profile's leagues come back directly). Needs: Sleeper username + season; ESPN espn_s2 + swid + season + sport; Fantrax secret_id. Fantrax discovery often returns empty even when leagues exist: then ask for a league URL/id and use the league tools directly.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
sportNoe.g. 'NFL', 'NBA'. Needed for ESPN/Sleeper and Fantrax name lookups.
seasonNoSeason year, e.g. 2025; ignored by Fantrax.
providerNoFantasy platform. Optional: defaults to your connected platform ('sleeper').
credentialsNoOnly WITHOUT a connected profile: secret_id (Fantrax), espn_s2 + swid (private ESPN), username or user_id (Sleeper discovery). Public ESPN and Sleeper reads need none.
response_formatNo'markdown' (default, most compact) or 'json' (same normalized data, not the raw payload).markdown

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed4 schema fields changed
    • changedInput schema / properties / credentials / description
      Previous value: -"Per-call credentials, only needed WITHOUT a connected profile. Keys: secret_id (Fantrax); espn_s2 + swid (private ESPN leagues); username or user_id (Sleeper discovery); session_cookie / auth_token + write_enabled:true (explicit write opt-in only). Public ESPN leagues and all Sleeper reads need none."New value: +"Only WITHOUT a connected profile: secret_id (Fantrax), espn_s2 + swid (private ESPN), username or user_id (Sleeper discovery). Public ESPN and Sleeper reads need none."
    • changedInput schema / properties / response_format / description
      Previous value: -"'markdown' (default) or 'json' (raw payload)."New value: +"'markdown' (default, most compact) or 'json' (same normalized data, not the raw payload)."
    • changedInput schema / properties / season / description
      Previous value: -"Season year, e.g. 2025. Required for ESPN/Sleeper league discovery; ignored by Fantrax."New value: +"Season year, e.g. 2025; ignored by Fantrax."
    • changedInput schema / properties / sport / description
      Previous value: -"Sport, e.g. 'NFL', 'NBA', 'MLB', 'NHL'. Required for ESPN/Sleeper and Fantrax name lookups."New value: +"e.g. 'NFL', 'NBA'. Needed for ESPN/Sleeper and Fantrax name lookups."
  2. Changed12 schema fields changed
    • changedInput schema / properties / credentials / additionalProperties
      Previous value: -falseNew value: +true
    • changedInput schema / properties / credentials / description
      Previous value: -"Per-call credentials. Fill only the keys your provider needs (see fantasy_list_providers). Public ESPN leagues and all Sleeper reads need none."New value: +"Per-call credentials, only needed WITHOUT a connected profile. Keys: secret_id (Fantrax); espn_s2 + swid (private ESPN leagues); username or user_id (Sleeper discovery); session_cookie / auth_token + write_enabled:true (explicit write opt-in only). Public ESPN leagues and all Sleeper reads need none."
    • removedInput schema / properties / credentials / properties / espn_s2
      Removed value: -{
-  "description": "ESPN private-league cookie 'espn_s2' (DevTools → Application → Cookies → espn.com).",
-  "type": "string"
-}
    • removedInput schema / properties / credentials / properties / secret_id
      Removed value: -{
-  "description": "Fantrax Secret ID (User Profile → 'Your Secret ID').",
-  "type": "string"
-}
    • removedInput schema / properties / credentials / properties / swid
      Removed value: -{
-  "description": "ESPN private-league cookie 'SWID': a GUID in curly braces, e.g. {XXXX-...}.",
-  "type": "string"
-}
    • removedInput schema / properties / credentials / properties / user_id
      Removed value: -{
-  "description": "Sleeper numeric user_id (alternative to username).",
-  "type": "string"
-}
    • removedInput schema / properties / credentials / properties / username
      Removed value: -{
-  "description": "Sleeper username (for league discovery).",
-  "type": "string"
-}
    • changedInput schema / properties / provider / description
      Previous value: -"Fantasy platform: 'fantrax', 'espn', or 'sleeper'. Call fantasy_list_providers first to see each provider's capabilities and required credentials."New value: +"Fantasy platform. Optional: defaults to your connected platform ('sleeper')."
    • changedInput schema / properties / response_format / description
      Previous value: -"Output format: 'markdown' (default, human-readable) or 'json' (raw upstream payload)."New value: +"'markdown' (default) or 'json' (raw payload)."
    • changedInput schema / properties / season / description
      Previous value: -"Season year, e.g. 2024. REQUIRED for espn and sleeper league discovery; ignored by fantrax."New value: +"Season year, e.g. 2025. Required for ESPN/Sleeper league discovery; ignored by Fantrax."
    • changedInput schema / properties / sport / description
      Previous value: -"Sport, e.g. 'NFL', 'NBA', 'MLB', 'NHL'. Required for ESPN/Sleeper and for Fantrax player/name lookups."New value: +"Sport, e.g. 'NFL', 'NBA', 'MLB', 'NHL'. Required for ESPN/Sleeper and Fantrax name lookups."
    • removedInput schema / required
      Removed value: -[
-  "provider"
-]
  3. First observed

TDQS

A4.3/5.0
Behavior4/5

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

Annotations already declare this a safe read (readOnly, idempotent, non-destructive, open-world), so the safety profile is covered. The description adds the non-obvious auth requirements per provider and the important quirk that Fantrax discovery can return empty even when leagues exist. No mention of rate limits or result shape, but the auth/edge-case disclosure is the valuable part.

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?

Dense but front-loaded: the primary case (no connected profile) leads, followed by provider requirements, then the failure fallback. Telegraphic phrasing ('Needs: ...') is efficient, though the credentials sentence is somewhat cryptic without the schema in view.

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?

With no output schema, the description still does not describe what a successful result looks like (a list of leagues with ids), though that is inferable. Given annotations cover safety and the schema covers parameters, the credentials prerequisites and Fantrax edge case make it nearly complete for a read/discovery tool.

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 description coverage is 100%, so all five parameters (including the nested credentials object and enums) are already documented in the schema. The description largely restates the provider-to-credential mapping and that Fantrax ignores season, adding little syntax or format detail beyond the structured data.

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 and resource ('Discover an account's leagues on a provider') and immediately scopes it against the sibling behavior of connected-profile reads. An agent can distinguish it from fantasy_get_my_teams/get_my_setup without opening any 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?

Gives per-provider prerequisites (Sleeper username+season, ESPN espn_s2+swid, Fantrax secret_id) and an explicit fallback path when Fantrax returns empty: 'ask for a league URL/id and use the league tools directly.' When-to-use and what-to-do-on-failure are both spelled out.

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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