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

Annotations already cover readOnlyHint and openWorldHint, so the safety profile is clear. The description adds real behavioral detail beyond that: a concrete credit cost ('15 per call') and a downstream dependencies hint about the returned `id`. It stops short of return shape or caching/rate behavior, so not 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 tight sentences, front-loaded with purpose, then param format, then cost and chaining. Every sentence earns its place with no repetition of structured data.

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 must cover returns — and it lists the profile fields plus the `id` needed for chaining. Combined with the cost note and param format guidance, an agent has everything required to call this correctly.

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 0%, so the description carries full burden — and it does: 'Pass userName = the handle without @ (e.g. "jack")' gives exact format and a concrete example. This fully compensates for the undocumented schema property.

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 — 'Look up a single profile by its @handle' — and enumerates the returned fields (bio, counts, verification state, avatar, banner). The word 'single' implicitly separates it from the batch sibling user_batch_info_by_ids without needing to name it.

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 rather than stated: the chaining hint 'The returned `id` is what tools taking userId need' tells the agent this is the entry point for userId-based tools, which is genuinely useful. However, there is no explicit when-to-use or when-to-prefer-an-alternative guidance against siblings like user_about or user_search.

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