Join Match

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

The description adds substantial behavior beyond the annotations: authentication flow, HTTP attempt count, revision-conflict handling, result conflicts, expired sessions, missing API key, rate limits, and return shape. Although annotations already declare the safety profile, the description provides unusually rich operational context without clearly contradicting readOnlyHint=false, openWorldHint=true, idempotentHint=true, or 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.

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

The description is long but structured and front-loaded, with labeled Use, Not for, Requires, Side effects, Returns, and Errors sections. Most sentences carry relevant operational detail, though the side-effects list includes behavior for other match operations that may not belong to this tool and slightly increases cognitive load.

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

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

For a complex authenticated write operation with no output schema, the description covers the missing return shape, error semantics, authentication prerequisites, conflict handling, and side effects. An agent has enough context to invoke it correctly and interpret common failure modes.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline would be 3, but the description adds meaningful semantics by linking sign-in to sessionToken and explaining that expectedRevision must remain the original reviewed revision. It adds less detail for matchId and userId beyond the schema, but the auth and revision guidance is useful.

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

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

The first sentence names a specific operation and concurrency condition: "Executes join match under the exact original revision." That is clear enough to identify the resource and action, though the side-effects section also describes start, turn, timeout, leave, and cancel behavior, which blurs whether this tool performs those operations or merely relates to them.

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

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, including exclusion of polling, traversal, timeout progression, invented winners, and automatic rewards. It also names horizon_get_matches and horizon_get_match for reconciliation, but it does not explicitly distinguish join_match from sibling mutations such as start_match, submit_match_turn, or leave_match.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.