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

Annotations already declare readOnlyHint=true, and the description reinforces this with 'Nothing is created or charged,' which is exactly the kind of side-effect disclosure an agent needs before quoting a cost. It also documents the return payload (person_count, estimated_credits). It stops short of richer traits such as whether the estimate is cached or how long it takes, so it is strong but not exhaustive.

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 core action in the first line and uses tagged sections for summary and returns, with no filler. The wording is dense but each sentence carries a distinct fact (what it estimates, when to use it, what it costs the caller). Slightly heavy for the amount of content, keeping it at a 4.

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?

Although there is no output schema, the description supplies a returns section naming the dict keys, and the summary covers usage, safety, and the pre/post-creation alternative. Combined with 100% schema coverage for the three optional parameters, an agent has everything required to invoke and interpret this call.

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 100%, so the schema already carries full parameter semantics, including the cross-references to list_classifiable_campaigns and list_agency_clients. The description only indirectly gestures at the parameters ('people it would tag', 'campaigns the segment would track'), so the baseline 3 applies rather than a higher score.

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 ('estimate the first classify run of a segment group that doesn't exist yet') and immediately bounds the scope to people tagged and credits charged for tracked campaigns. It explicitly distinguishes itself from the sibling classify_segment_group, which returns the exact figure for an existing group, so an agent can pick correctly without opening a 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 an explicit when-to-use ('tell the user the cost before creating the group') and names the alternative plus the condition that selects it ('once the group exists, classify_segment_group returns the exact figure for its run'). The pre-creation vs post-creation boundary is unambiguous.

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