get_v1_user_by_username

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

Annotations already declare readOnly/openWorld/non-destructive, and the description adds real value beyond them: it is a live request, billed per call, may return 404 ProfileUnavailable, and the returned user object carries the secUid needed by the by-secUid tools. That chaining and cost context is exactly what annotations cannot convey.

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, all load-bearing: purpose, fallback routing, return/chaining plus cost. The endpoint annotation is appended compactly and nothing is repeated from structured fields.

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?

No output schema exists, and the description covers the return value ('the user object'), the key field to extract (secUid), the error case, and the cost model. Nothing an agent needs to invoke or chain this call 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?

Only one parameter with 0% schema description coverage, so the description must compensate. It does so meaningfully by specifying the format constraint '(without @)', which the schema's bare string type does not express, though it omits the 2–24 length bounds.

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 ('Get a TikTok profile by username') and explicitly distinguishes itself from the sibling get_v3_user_by_username by naming the fallback relationship. An agent can tell the two apart without opening 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?

Gives an explicit ordering rule ('Use it first for any account') plus the exact trigger for switching tools ('404 ProfileUnavailable'), naming the alternative. Both when-to-use and when-to-switch are spelled out.

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