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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description still adds real context: data is cached/offline rather than live, the miss case returns 'User not found', and results are user-generated untrusted input. It does not discuss rate limits, but for a single-row lookup that is minor.

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 tightly packed sentences with zero filler, front-loaded with what the tool does and its data-source caveat. Slightly longer than strictly needed, but each clause (source, alternatives, return shape, untrusted warning) carries distinct information.

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-param lookup with no output schema, the description still conveys the return shape (same full profile row as `get_user_by_username`, or 'User not found') plus the trust caveat. Nothing an agent needs to invoke or interpret the 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?

Schema coverage is 100% and the single `id` parameter is already documented as the Instagram user ID (pk). The description adds where the value comes from (another tool's output) and the alternate lookup routes, but no format or edge-case detail beyond that. Baseline 3 is appropriate.

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 (get) plus resource (Instagram profile by numeric pk) and explicitly scopes the data source: the DataLikers database, 'not a live Instagram fetch.' It also contrasts itself against the two nearest siblings, so an agent can pick the right tool 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 routing rules: use this for a pk taken from another tool's results, use `get_user_by_username` for a handle, and `get_users_by_ids` for up to 100 pks. When-to-use and alternatives are both spelled out, leaving nothing to inference.

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