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

Annotations cover only readOnly/openWorld, so the description carries real added weight: it discloses that raw support statements, arrays, false/null and unresolved mirrors are preserved verbatim and that versions must never be inferred. It also reveals two costly operational facts an agent must know before calling — a $0.01 USDC per-successful-call charge on Base and the requirement for an x402-capable wallet client.

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 description is front-loaded with the core action and scope, followed by behavioral constraints and then the critical payment/auth requirements. It is dense but every clause earns its place; slightly more packing than ideal, but no filler.

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 steps in to describe return semantics (preserved support statements, arrays, false/null, unresolved mirrors), and it discloses the payment and wallet prerequisites. For a 2-parameter read tool with payment gating, 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?

Schema description coverage is 100%, so both parameters (the enum-constrained browser and the exact BCD feature path) are already fully documented in the schema. The description only reinforces exactness ('one exact ... feature and browser') without adding format or syntax detail beyond the schema, so the baseline of 3 applies.

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 ('look up') and resource ('one exact MDN BCD feature and browser'), with the important scope constraint that it is a single exact lookup against the actor pinned release and verified Git blob. It does not explicitly name or contrast with the nearest sibling (software-support-lookup), so it stops short of 5.

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?

The phrase 'one exact ... feature and browser' and 'never infer versions' imply this is for precise, single-point data retrieval rather than bulk or inferred queries. However, there is no explicit when-to-use/when-not-to-use guidance and no named alternative to route to, leaving usage context inferred.

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