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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), and the description adds genuinely new operational facts: 1 credit per call, one profile per call, and a hard plan-gating rule that produces an error for trial keys. That billing and access information is exactly the kind of context 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?

Three short sentences, front-loaded with the core action and return fields, then cost, then access restriction. Every sentence carries distinct information with no redundancy.

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 compensates by enumerating the returned fields, and it also states cardinality (one call, one profile), cost, and plan gating. For a two-parameter read tool, an agent has everything needed to decide and invoke 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 both parameters (username, user_id) are already documented with format examples in the schema. The description adds no meaning about the anyOf either/or requirement or when to prefer user_id over username, so it stays at the baseline for a fully-documented two-parameter schema.

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 opens with a specific verb and resource ("Get an X (Twitter) user's public profile") and immediately enumerates the returned fields (followers, following, bio, verified status). It also implicitly distinguishes itself from the tiktok_profile sibling by naming the platform scope and noting the trial tier is TikTok-only.

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?

It gives a clear eligibility condition for use: paid plans and pay-as-you-go only, with trial keys receiving an error. It does not, however, route the agent between x_profile and x_search (e.g., search by keyword vs. fetch a known handle), so alternative selection is left to inference.

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