instagram_user_id

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

Annotations already establish readOnly and openWorld safety, so the bar is lower. The description adds a genuinely useful behavioral trait not present in structured data: a billing cost of 1 credit, plus the note that the operation is rarely needed.

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 and terse, with the practical guidance and cost separated cleanly. The first two sentences slightly restate each other ('username to user id' / 'numeric user id for a handle'), a minor redundancy that prevents a 5.

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 simple, optional-parameter read tool with no output schema, the description covers purpose, usage context, and cost adequately. Nothing critical is missing, though the response format is not described (acceptable since no output schema exists).

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 both parameters (user_id and username, including the @ handling and URL acceptance) are fully documented in the schema. The description adds no syntax or format detail beyond what the schema already provides, so baseline 3 applies.

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 transformation (username/handle -> numeric user id), which is a clear verb-resource relationship an agent can act on. It doesn't explicitly differentiate itself from the sibling instagram_username tool, so it stops short of a 5, but the purpose is unambiguous.

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?

Provides clear when-NOT-to-use guidance: 'Every endpoint also accepts either one directly, so you rarely need this.' This steers the agent away from unnecessary calls, though it stops short of naming a specific alternative tool to use instead.

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