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

Annotations already declare destructiveHint=true/openWorldHint=true, but the description goes further by disclosing a concrete failure mode (INVALID_ARGUMENT when AUTO groups already exist because Amazon pre-created them) and the precondition that AUTO groups are immutable via this tool. That is meaningful behavioral context beyond the annotations.

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?

Front-loaded with the core action, then branches cleanly into MANUAL/AUTO, then a warning, then an alternative. Each clause earns its place, though the inline enum glosses and the final reroute sentence make it dense for a single description.

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 mutation tool with no output schema, it covers payload shapes, error semantics, and the bid-change alternative well. It does not spell out the preview/confirm_id write flow (delegated to the schema description) or the return shape, leaving a small gap for a write operation.

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?

The schema defines 'targets' only as a bare array with no item schema, so the description carries the real burden and delivers it: exact field shapes for MANUAL targets ({campaign_id, ad_group_id, bid, one of asin/category_id/expression}) and AUTO targets (auto_match enum with all four values defined). This adds substantial meaning the schema does not provide.

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 ('Create SP targets') and then disambiguates the two campaign modes (MANUAL vs AUTO) that produce different target shapes, which no sibling tool covers. An agent can distinguish it from ads_create_sp_keywords, ads_create_sp_negative_targets, and ads_update_sp_target_bid from the text alone.

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?

Explicitly states when to use it (MANUAL campaigns with asin/category_id/expression; AUTO campaigns with auto_match groups) and when NOT to: re-creating the 4 AUTO groups on an existing campaign yields INVALID_ARGUMENT, and bid-only changes should route to ads_list_sp_targets + ads_update_sp_target_bid. This is a textbook when/when-not/alternative routing.

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