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

Annotations already flag destructiveHint=true and idempotentHint=true, so the safety profile is covered; the description adds real value beyond that by explaining the side effect (Meta re-paces the remaining lifetime budget, total cap unchanged) and the 24-hour constraint. It does not spell out what is actually lost/irreversible despite destructiveHint=true, so it is not a 5.

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-loads the action in the first clause, then layers budget semantics and the hard constraint, closing with 'WRITES live.' Every sentence carries information. It is dense with parentheticals but not padded.

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 3-param, all-required mutation with full schema coverage and no output schema, the description covers action, side effects, and a key validation rule. Missing only permissions/account-level prerequisites and any statement of failure behavior, which keeps it from a 5.

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 coverage is 100%, so baseline is 3; the description earns above that by adding a constraint on end_time that the schema lacks — with a lifetime budget the new end must be more than 24 hours after the ad set's start. It still says nothing extra about adset_id or meta_account_id, which the schema handles.

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 precise verb+resource+scope: 'Change the END time of an existing ad set' — deliberately narrow, updating only the end time, not budget or status. That scope cleanly separates it from siblings like update_campaign_budget and pause_campaigns without needing to name them.

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 a concrete motivating scenario ('start a fixed run once delivery is confirmed') and states a hard precondition for lifetime-budget ad sets (end must be >24h after start). It does not state when NOT to use this tool or point to an alternative, so it stops short of a 5.

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