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

Annotations already declare readOnly/destructive=false, and the description adds real behavioral context beyond that: the call is free and does NOT charge a credit, it requires Bearer auth, anonymous callers get a 401 with a signup link, and it needs a free StartupHub.ai account. These are exactly the operational facts an agent needs and that annotations cannot convey.

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-loaded with the resource and returned fields, then cost behavior, then usage guidance, then auth. Every sentence carries weight, though the parenthetical enumeration of all seven credit types is slightly list-heavy for the space it consumes.

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 zero-parameter read tool with no output schema, the description enumerates the returned fields, states the cost and auth requirements, and points to the correct next tool. Nothing an agent needs 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?

The tool takes zero parameters, so the schema carries no parameter semantics to explain and the baseline is 4. The description correctly adds no spurious parameter discussion.

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 ('Check the user's current credit balance') and enumerates exactly what is returned (plan tier, limits, used/remaining today and month, never-expiring pack balance). It is immediately distinguishable from data-consuming siblings like discover_email or enrich_company.

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?

Explicit when-to-use ('call before any expensive batch (e.g. 100x discover_email)') and names the follow-up alternative ('if they're low or ask to buy more, follow up with list_credit_packs to get pricing + a checkout URL'). Both the trigger condition and the sibling are given.

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