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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), so the description clears the lower bar comfortably by adding what the search actually matches on, what comes back (uid, username, displayName, photoURL), and an explicit privacy exclusion ('Never email or billing fields'). That privacy/data-scope statement is information annotations cannot express.

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?

Two sentences with no filler: purpose and match ordering first, return/withheld fields second. Every clause carries information an agent would otherwise have to guess.

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 takes on the return-value burden and discharges it by enumerating the returned fields and explicitly excluding sensitive ones. Parameters are fully documented in the schema and safety is covered by annotations, so nothing an agent needs to invoke this 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 description coverage is 100%, so the baseline is 3. The description goes beyond the schema's generic 'Username or display-name prefix' by specifying the match precedence and the underlying fields consulted, which clarifies how the required query parameter actually behaves. It does not touch limit/cursor/offset semantics, which the schema already handles.

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 ('Search public Instadram profiles') and, unusually, the exact match ordering (exact username match on usernames/{handle} or users.username first, then displayName prefix). This distinguishes it from siblings like get_user, check_username, and discover_users without naming them.

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 by the matching rule (you search by handle or display-name prefix), and 'public profiles' quietly scopes the tool away from private/deleted accounts. However, it never states when to prefer this over discover_users or get_user, nor any prerequisites, so guidance remains inferred rather than explicit.

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