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

Annotations cover the safety profile (readOnly=false, idempotent=true, destructive=false, openWorld=true), and the description adds genuinely useful behavior the annotations cannot convey: that spendCap is Meta's hard stop which halts all ad delivery once reached, that it is in whole currency units, and that null removes it. It stops short of stating reversibility of a rename or whether partial updates are allowed.

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?

Two tight sentences, front-loaded with the operations, then the one piece of non-obvious semantics. No filler; every clause carries information.

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, the description covers what changes and the consequence of spendCap well. The remaining gap is the ambiguous adAccountId vs accountId/profileId relationship (one required, two optional with defaults), which is left entirely to the schema.

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 40%, so the description must compensate. It adds real semantics for spendCap (currency units, null-to-remove, delivery consequence) beyond the schema's bare number/null constraint, but says nothing about adAccountId (which has only a pattern, no description) or how it differs from accountId/profileId. Partial compensation for the coverage gap.

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 (rename an ad account, set/remove its spending limit) and is clearly distinguishable from siblings like ads_create_account and ads_get_account. The two supported operations are enumerated up front.

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?

Usage is implied by naming the operations and by explaining the effect of spendCap, but there is no explicit when-to-use/when-not guidance and no routing to alternatives (e.g., ads_set_status for delivery toggling). Adequate but leaves the agent to infer context.

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