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

Annotations already declare destructiveHint=true, idempotentHint=true and openWorldHint=true, so the bar is lower, yet the description still adds value: patch semantics ('Only fields you pass change'), the verified-subscriber gate, and a pointer to automation side effects (email/text to subscriber or referrer) that can unlock rewards. It stops short of stating irreversibility or what happens on unverified subscribers.

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?

One tight block, led by the 'WRITE' severity marker, followed by fields, overwrite semantics, precondition, and endpoint. Every clause carries distinct information with no repetition.

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 17-parameter destructive mutation with no output schema, the definition covers scope, patch behavior, preconditions, side effects and endpoint. Remaining gaps are minor: no note on error behavior for unverified subscribers or on what is returned after the update.

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 description coverage is 100%, so the schema already documents all 17 parameters; the description only groups them into families and restates the qualified/unqualified enum and the contest-only constraint on points. With full schema coverage the baseline of 3 is correct.

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+resource ('change fields of a subscriber'), enumerates the mutable field families, and pins the exact endpoint POST /lists/{uuid}/subscribers/{id}. The 'WRITE' prefix and 'overwrites the given fields' make clear this is a partial-update mutation, not a create.

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?

Gives real preconditions: only verified subscribers can be updated, and points only apply to contest campaigns. It does not, however, route the agent away from near-neighbors such as referralhero_add_points or referralhero_qualify_referral/referralhero_unqualify_referral for the same effects.

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