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

Annotations already declare the mutation profile (readOnlyHint=false, destructiveHint=true, idempotentHint=true), and the description adds two non-structured facts: changes are additive/partial rather than full-replacement, and a tier/ownership gate applies. It doesn't say what a failed tier check or an invalid field returns, which is the remaining gap.

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 short sentences, front-loaded with the verb+resource, then the partial-update rule, then the field list, then the gate condition. Nothing is redundant with the title and no sentence is 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?

For a 7-parameter mutation with full schema coverage and no output schema, the description covers ownership, tier gating, and partial-update behavior adequately. It could be stronger by noting whether the updated program object is returned or noting rate-change side effects on existing partners.

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 every parameter (name, cpa_rate, cpc_rate, is_public, description, cookie_duration_days, program_id) is already documented with ranges and lengths in the schema. The description only re-lists the field categories without adding format, default, or clearing semantics, so it earns the baseline 3.

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 ("Update an affiliate program") and scopes it to programs "you own as a merchant", which cleanly separates it from create_affiliate_program, get_affiliate_program, and join/leave_affiliate_program. It also enumerates the editable fields, so an agent knows exactly what surface this tool touches.

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 clear preconditions — merchant ownership and "Builder tier or higher" — plus the important partial-update rule ("Only provided fields are changed"). It stops short of naming alternatives such as update_affiliate_partner_status or get_affiliate_program, so an agent must infer when this is preferred over those.

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