instagram_username

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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely novel behavior: a 3-credit cost and the fact that the returned handle stays valid after an account rename. That is useful operational context beyond the structured fields.

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 core transformation in the first fragment, followed by the useful rename caveat and cost. Short and largely waste-free, though the cost line reads as a tagged-on afterthought.

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 single-parameter read tool, the definition covers what it returns (the current handle), a behavioral caveat, and the credit cost. No output schema exists, but the description adequately characterizes the return value; only alternative-tool routing 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 user_id example and meaning are already documented, making 3 the baseline. The description adds only 'numeric user id' reinforcement, and the schema's 'Pass this or username' references a username parameter that the input schema does not actually contain.

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 directional transformation (numeric user id → current username handle), which is concrete and actionable. The id→handle direction implicitly contrasts with the reverse sibling instagram_user_id, but the description does not name that sibling explicitly.

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?

No when-to-use guidance and no exclusions. It does not explain when to prefer this over instagram_profile or instagram_user_id, both of which an agent might otherwise reach for. The rename-persistence note is a trait, not usage routing.

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