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

Goes well beyond the annotations by disclosing the payment model ($0.003/call via x402 USDC or card key, first 25 free, failed calls free) and explicitly reconciling the readOnlyHint=false annotation (compute-only, but not marked read-only because each call is charged). This is exactly the kind of non-obvious behavior an agent needs.

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 is front-loaded in the first clause, and each subsequent sentence adds distinct information (modes, trigger context, pricing, read-only rationale). The mid-sentence example is slightly awkward, keeping it from a 5.

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 one-parameter compute tool with annotations covering the safety profile, the description covers purpose, payment, and the read-only caveat. The only minor gap is that the return value (the encoded string) is not stated, but with no output schema and such a trivial result this is nearly negligible.

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?

Only one parameter and schema description coverage is 100%, so the schema already documents "text." The inline example (text=a b&c=d/é) hints at input shape but is not formal syntax or format guidance beyond what the schema provides; baseline 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 (percent-encode) and resource (text for URLs), and distinguishes the two modes: encodeURIComponent for query values vs encodeURI for full URLs. This lets an agent tell what it does apart from siblings like url_decode and url_parse 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 context: "Use when building query strings," plus the two supported output modes. It does not name url_decode as the inverse alternative or exclude any scenarios, so it is clear but lacks the exclusions/alternatives that would earn a 5.

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