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

Annotations already cover the safety profile (readOnly, idempotent, closed-world), but the description adds real behavioral value: it is a 'Supabase-only read so it's instant' and a 'single-call snapshot,' which tells the agent about cost/latency versus the slower Google-API sibling. It stops short of noting auth requirements or error behavior, 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?

The purpose and scope are front-loaded in the first clause, and the usage cues follow in question form. The long mid-sentence field enumeration is dense, but since there is no output schema it is load-bearing rather than filler; it could still be tightened slightly.

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 no-parameter, no-output-schema read tool, the description substitutes for the missing output schema by enumerating the returned fields (email, admin flag, MCC, brand count/limit, campaign counts, reports, plan tier, trial days) and covers usage and cost. Nothing an agent needs to select or 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?

The tool takes zero parameters, so there is no parameter semantics burden and the baseline is 4. The description's field enumeration is about return values, not inputs, so nothing further is owed here.

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 ('return a single-call snapshot of this user's Upfixe state') and enumerates exactly what the snapshot contains. It also names a sibling (list_ad_accounts) and explains why this tool differs, so an agent can distinguish it without opening schemas.

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 explicit trigger questions ('what's my MCC?', 'which plan am I on?', 'how many brands do I have?') and an explicit when-not clause routing the agent away from list_ad_accounts for MCC introspection. Both use and anti-use conditions are spelled out.

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