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

Goes well beyond the annotations: the Role is spent and the action cannot be undone, already-paid sessions are unaffected, and specific HTTP-style failure codes are disclosed. These details are consistent with destructiveHint=true and idempotentHint=true, and add the cost/irreversibility context the annotations alone can't convey.

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?

Four tight sentences, front-loaded with the action and the spending/irreversibility constraint, then the idempotent edge case, then return value and errors. No filler.

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?

Despite no output schema, the description states what is returned (sessionId) and the failure conditions (402, 403). Combined with the behavioral constraints, an agent has everything needed to invoke it correctly and interpret the outcome.

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?

There is one required parameter at 0% schema description coverage. The description implies the sessionId must reference an 'owned sourcing session' and that sessionId is returned, but never explains the parameter itself. It partially compensates for the coverage gap but leaves the parameter's expected format unstated.

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?

States a specific verb and resource: assign a paid Role to a sourcing session to unlock paid access. The title and description together make clear this is a state-mutating unlock, distinct from the other sourcing_* siblings that contact, continue, read, or stop sessions.

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?

Explains the condition under which it applies and the no-op case ('a session that is already paid keeps its Role and no other is spent'), plus the failure conditions (402 no Role, 403 unverified email). It doesn't name a sibling alternative, but the action is unambiguous enough that no alternative is plausible.

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