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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description goes beyond them with operational detail: stateless, 32 KB max payload, 60 RPM, demo=true or L402 payment of 15 sats, and HTTP 400 on invalid input — exactly the auth/limit/error context annotations cannot express. Slightly dense but substantive.

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?

Purpose and the sibling alternative are front-loaded in the first two clauses. The trailing operational sentence packs rate limits, payment, and error codes into one parenthetical chain, which is efficient but slightly overloaded for a single sentence.

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?

An output schema exists, so return values need no explanation; the description instead covers the limits, payment/auth path, and failure mode an agent needs before calling. For a two-parameter tool this is complete.

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% and both properties carry descriptions and an enum, so the schema does the heavy lifting. The description only restates that 'description' is accepted and that 'flavor' defaults to 'ecmascript_js', which the schema already says — baseline 3.

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 ('Synthesizes linear-time O(n) regular expressions') plus a second action ('validates them against positive and negative test strings'). The property claimed (ReDoS-free, O(n)) is the discriminating trait versus siblings, and it names heal_malformed_json as the alternative.

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 use case is given ('generating and verifying a regular expression pattern for input validation or lexical parsing') along with an exclusion and the tool to use instead ('for repairing broken JSON syntax directly... use heal_malformed_json'). Nothing is left to inference about when to pick this tool.

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