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

Annotations already declare destructiveHint=true and openWorldHint=true; the description adds genuinely new behavior: partial-merge semantics, full-replacement overwrite semantics for the targeting object, and the fact that widening the audience returns a preview gated by confirm=true. It does not spell out that a full replacement discards existing targeting or what permissions are required, leaving some risk unstated.

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?

Three dense sentences, front-loaded with the action and the most consequential rule (partial vs. full replacement). Every clause carries information an agent needs; there is no filler or restatement of the title.

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 destructive 13-parameter mutation with a nested object and no output schema, the description covers the mechanics that matter: incremental vs. replacement, and the preview/confirm gate on widening. It is slightly incomplete on account/folder scoping and on what the non-preview response contains.

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 only 38%, so the description must carry weight, and it does for the core fields: countries are ISO codes, os takes iOS/ANDROID/WEB, add_segments/remove_segments are additive/subtractive audience IDs, and targeting is a full replacement. It leaves account, folder, language, and adsquad undocumented, which is a real gap at 13 parameters.

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 description opens with a specific verb+resource ('Change an ad squad's targeting') that cleanly separates it from sibling tools like snapchat_create_adsquad, snapchat_update_bid, and snapchat_update_schedule. It also enumerates the targetable fields, so an agent knows exactly what kind of change this tool performs without opening the schema.

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?

'Pass only what changes' vs. 'a full Snap targeting object to replace it' gives explicit guidance on the two operating modes and when to pick each. It also states the precondition for the preview path (widening needs confirm=true). It stops short of naming alternative tools or stating when not to use this one, so it falls just under a 5.

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