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

Annotations only cover the safety profile (readOnly, non-destructive, closed-world), so the description adds genuinely new behavior: no in-MCP purchase path, browser-only checkout, credits never expire, and volume discounts auto-apply. It also sketches the return shape, which is valuable given no output schema exists.

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 purpose and keeps the usage trigger and purchase-flow caveat tight. The inline return JSON and hardcoded URL are slightly heavy, but each sentence carries usable information for a tool with no output schema.

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?

With no output schema, the description correctly supplies the return structure (buy_url + pricing tiers) and the credit terms. Nothing an agent needs to call it or relay results to the user 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 coverage is 100%, so the baseline is 3, but the description goes further by showing pricing organized as { validate: [...tiers], discover: [...tiers] }, tying the enum values to concrete output categories and clarifying what the 'type' parameter selects.

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 ('Get credit pack pricing AND a checkout URL') and expands on the name to include the buy_url, so an agent immediately understands the dual output. No sibling tool overlaps this pricing/credits purpose, so differentiation is implicit but unambiguous.

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 trigger: surface buy_url on a 402 'credit_limit_exceeded' error, or when the user asks 'how do I get more credits'. It also sets a hard boundary ('no in-MCP purchase flow; Stripe checkout requires a browser'), leaving nothing to inference.

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