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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower, yet the description adds substantial behavioral context: the ARCHIVED = DELETED semantic, that archived items are excluded by default with archived_count as the signal, and that never_fired entries are live but have never recorded a conversion. It even warns the agent not to present never_fired conversions as working, which is meaningful interpretation guidance beyond structured fields.

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 what the tool does, then adds two targeted paragraphs on archived and never_fired semantics. Every sentence carries information, though three paragraphs is on the long side for a two-parameter list tool and the final sentence is mildly editorial.

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?

An output schema exists, so return values need not be documented, and the description still surfaces the two fields an agent must interpret (archived_count, never_fired). For a read-only listing tool with annotations covering safety, nothing needed to call it correctly is missing.

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 0%, so the description carries the burden. It fully explains include_archived (default exclusion, archived_count, when to set true), which adds real meaning beyond the bare boolean in the schema; account_id is left implicit but is self-evident from the name.

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 ('Lists the account's custom conversions') and immediately defines the resource ('URL- or event-based conversion definitions built on a pixel, e.g. visited /thank-you'), which lets an agent distinguish it from list_meta_pixels or create/update_meta_custom_conversion. The purpose is unambiguous 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?

Gives clear conditional guidance for the one non-obvious input: pass include_archived=true 'only when the user asks about deleted ones'. It also frames why the resource matters ('use one for reporting or as an ad set's optimization event'). No sibling tool is named as an alternative, so it stops short of a full when/when-not/alternatives statement.

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