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

Beyond the readOnly/idempotent annotations, it discloses that the data comes from a static database and not a live fetch, that a miss returns 'User not found', what the payload contains, and warns that the content is user-generated and should be treated as untrusted input. That untrusted-input caution is a meaningful behavioral disclosure 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?

Front-loaded with the action and source-of-truth distinction, then routing, then return shape, then the safety note. Dense but every clause earns its place; only slightly long compared to an ideal single-line routing statement.

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 steps in to describe the return payload (counts, biography, category, contact info, face-analysis fields) and the not-found case. An agent has everything needed to call and interpret 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 coverage is 100% and the single parameter is documented, so the baseline is 3. The description adds real value beyond the schema by specifying the lookup is case-insensitive and that the leading '@' must be stripped, details the schema text does not carry.

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+resource ('Get one Instagram profile by exact username') and immediately scopes it as a DataLikers database lookup rather than a live Instagram fetch. This distinguishes it cleanly from siblings like get_user_by_id and search_users without needing to open any 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?

Explicitly states when to use it ('when you know the handle') and names three concrete alternatives with their selecting conditions: get_user_by_id for numeric pk, search_users for partial names, get_users_by_ids for many pks. This is textbook routing guidance.

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