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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=true). The description goes beyond them by disclosing a per-call cost of 2 credits and a durability trait (the handle remains valid across account renames), both of which materially affect tool selection. It stops short of describing failure behavior for unknown ids.

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 short sentences, front-loaded with the operation and followed by the value proposition and cost. Nothing is padded. Minor redundancy between the title and the opening clause, which costs it a point.

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-parameter lookup with no output schema, the description supplies the essential return value (the current handle) plus cost, and annotations carry the read-only/open-world profile. It is nearly complete; absent are not-found behavior and any tie-breaking against the reverse-lookup sibling.

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%, so the single user_id parameter is already fully documented with type, example, and the note 'Pass this or username.' The description only reinforces that the id is numeric, adding no syntax or format detail beyond the schema. Baseline 3 applies when the schema does the heavy lifting.

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?

The description states a specific transformation: a numeric user id maps to the current handle. It adds a meaningful qualifier (the handle stays valid after renames), which sharpens what the tool actually returns. It does not, however, distinguish itself from the reverse-direction sibling instagram_user_id, so the differentiation is left to the agent.

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?

There is no statement of when to use this rather than instagram_user_id (the obvious reverse lookup) or instagram_profile. The phrase about surviving renames hints at a use case but never frames it as guidance. The agent gets no exclusions or alternative routing.

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