League Loom

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

Name	Required	Description	Default
`sport`	No	e.g. 'NFL', 'NBA'. Needed for ESPN/Sleeper and Fantrax name lookups.
`season`	No	Season year, e.g. 2025; ignored by Fantrax.
`provider`	No	Fantasy platform. Optional: defaults to your connected platform ('sleeper').
`credentials`	No	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.
`response_format`	No	'markdown' (default, most compact) or 'json' (same normalized data, not the raw payload).	markdown

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 24, 2026

changedInput schema / properties / credentials / additionalProperties
```
Previous value: -trueNew value: +{}
```

changedInput schema / properties / season / anyOf

Previous value: -[
-  {
-    "type": "integer"
-  },
-  {
-    "type": "string"
-  }
-]New value: +[
+  {
+    "maximum": 9007199254740991,
+    "minimum": -9007199254740991,
+    "type": "integer"
+  },
+  {
+    "type": "string"
+  }
+]

Changed4 schema fields changedSep 29, 2026

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."

Changed12 schema fields changedSep 10, 2026

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"
-]
```

First observedJun 29, 2026

TDQS

A4.4/5.0

Behavior4/5

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

Annotations already declare readOnly/idempotent/non-destructive/open-world, so safety is covered; the description adds real value by enumerating which credential each provider requires and by warning that Fantrax discovery frequently returns empty even when leagues exist. That caveat is exactly the kind of failure-mode disclosure annotations cannot carry. It does not say what happens on partial credential failures or whether an empty result is otherwise distinguished from an error.

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 purpose followed by prerequisites and a fallback note; every sentence carries information. The telegraphic 'Needs: ...' colon-list is efficient but slightly compressed, reading more like notes than prose.

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?

For a 5-param, zero-required, multi-provider discovery tool with no output schema, the description covers the decision point, per-provider inputs, the optional provider default, and the known empty-result trap — nothing an agent needs to call it correctly 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 100%, so baseline is 3; the description earns above that by mapping parameters to providers (Sleeper username + season; ESPN espn_s2 + swid + season + sport; Fantrax secret_id) and noting Fantrax ignores season — cross-parameter relationships the per-field schema text does not express.

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') and immediately scopes it against the connected-profile path (fantasy_get_my_teams-style), so the agent can distinguish it from the many league-read siblings 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 Guidelines4/5

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

Gives a clear primary condition ('mainly WITHOUT a connected profile') and a contrast case ('a connected profile's leagues come back directly'), plus a concrete fallback when Fantrax returns empty (ask for a league URL/id and use league tools directly). It stops short of naming the specific alternative or fallback tools, which is what a 5 would require.

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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