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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world behavior, so the safety profile is covered. The description adds genuinely non-structured behavior: it forbids guessing the id and mandates a human confirmation loop plus recording the result in the project's Twinr section. It stops short of describing failure behavior for a stale or unknown app_id, which keeps it from a 5.

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?

Three sentences: what it returns, the fallback procedure, the anti-inference rule and the record step. Payload comes first and every clause is actionable; no filler or restatement of the title.

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 single-parameter, read-only lookup with a full output schema and full annotations, the definition covers invocation, prerequisite discovery, fallback path and post-call bookkeeping. Nothing an agent needs in order 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 coverage is 100%, so the baseline is 3, and the description goes beyond the schema by naming the value's source ('application_id recorded in this project's Twinr section' / replit.md on Replit, otherwise AGENTS.md). That provenance is real added meaning the schema property only gestures at. It adds no format, length or error-handling guidance for the id itself.

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 first sentence names a specific verb plus resource ('Get one Twinr app's details') and enumerates the returned fields: name, organization, website, platform and store identifiers. That level of specificity distinguishes it from list_apps without the agent needing to open either schema.

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?

It gives an explicit condition ('If this project's Twinr section ... has no application_id'), a named alternative ('call list_apps'), a concrete next step (show the merchant every organization and its apps, then ask), and two prohibitions ('never choose one yourself', 'never infer it from the project's name or URL'). This is the strongest tier of routing guidance.

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