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

Annotations already declare readOnlyHint and destructiveHint, so the safety profile is covered. The description adds meaningful behavior beyond that: case-insensitive matching is handled server-side, the @ sign should be omitted by the caller, and the tool returns both the profile record and the underlying creator record. This gives an agent useful expectations beyond the structured annotations.

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?

The description is front-loaded with the core purpose, then gives usage conditions, input formatting rules, exclusions, and concrete examples. Although it is longer than average, every sentence earns its place by either clarifying invocation or routing the agent to the correct sibling tool.

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 two-parameter read-only tool with a full input schema and an output schema, this description covers everything an agent needs: when to use it, how to format inputs, what it returns, and which alternatives to use in related cases. There are no material gaps.

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 baseline is 3; the description adds extra meaning by explaining how to pass the username exactly as typed without the @ sign, that matching is case-insensitive, and how to parse a URL into platform and username. This is genuinely useful clarification beyond the schema descriptions.

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: 'Fetch a single social profile by (platform, username).' It clearly distinguishes itself from siblings by naming exact-use cases, the canonical creator ID, and what data is returned. This leaves no ambiguity about what the tool does.

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 explicit when-to-use guidance ('Always use this first when the user gives an exact handle'), explicit when-not-to-use guidance ('Do not use search_creators'), and names concrete alternatives for other situations: get_creator for an already-known UUID and lookup_profiles for batch lookups. This is model-level routing guidance.

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