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

With no annotations, the description carries the burden well: it discloses the fallback rule for unregistered tools (assumed cost 0), that the call itself is free, and the exact return payload shape. It doesn't mention auth requirements or limits on how many tools can be estimated.

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 tight sentences: what it returns, the second input mode with examples, and the output/fallback behavior. Zero filler and the core purpose is front-loaded.

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?

Covers purpose, both input modes, return fields, and the unknown-tool fallback, which is thorough for a no-output-schema tool. Minor gaps: the reserved 'params' object and the semantics of 'sufficient'/'balance' are not explained.

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 baseline is 3, but the description adds value beyond the schema by enumerating all six valid stream type strings (external_profile, company, topic, person_interests, hiring_signals, ad_watch), whereas the schema only gives 'e.g. external_profile'. The unused 'params' object is not discussed.

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 verb and resource ('Given an MCP tool name, return its credit cost') plus a second accepted input mode (stream types). It is clearly distinguishable from siblings like get_credit_balance (which presumably reports current balance) and get_usage_history.

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?

Explains the motivating use case ('preview an action before running it') and ties the stream-type mode to create_stream / run_stream_now. It never states when to use get_credit_balance or get_usage_history instead, so the routing guidance is clear but not exhaustive.

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