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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds one extra behavioral trait – validation performed 'as you type' – which goes beyond the annotations and helps set expectations about input checking. It does not repeat or contradict the annotations.

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 first sentence is compact and front-loads the purpose. The second sentence, 'A HelpySelf tool (helpyself.com),' is brand attribution that gives an agent no selection or invocation value, so the description doesn't fully earn its length.

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 a rich parameter schema and safety annotations, the description doesn't need to explain parameters or safety, and it does state the core purpose. However, it never mentions what the tool returns (the assembled URL string), and there is no output schema to fill that gap, so the description alone leaves that question open.

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%, with each parameter explained in detail (e.g., url's replace-and-keep behavior, normalise's default and rationale, source's pasted-URL flag). The description itself adds no parameter-level information, so it stays at the baseline 3 since the schema already carries the heavy lifting.

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?

The phrase 'A UTM builder for campaign URLs' states the resource (campaign URLs) and the function (UTM tagging), and the clause about catching tagging mistakes highlights a distinctive behavior. It lacks an explicit imperative verb such as 'build', and there is no sibling UTM tool to differentiate from, so it just misses the 5-level specificity.

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?

Usage is implied by the noun-phrase description: this is the tool to call when a campaign URL needs UTM parameters. There is no explicit when-to-use or when-not-to-use guidance and no named alternative among the 100+ siblings, but the purpose is clear enough that an agent can infer the intended case.

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