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

Annotations already provide readOnlyHint=true, idempotentHint=true, destructiveHint=false. The description adds valuable context: 'Every call is read-only and idempotent, so after correcting the input it is always safe to retry' and describes the non-error-raising behavior ('returns {"error": ...}'). No contradiction with 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 concise with three focused paragraphs: purpose/platforms, input/output example, and usage/error handling. Every sentence provides necessary information with no redundancy or fluff.

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?

Given the tool's simplicity (one parameter, clear output schema), the description covers purpose, platforms, usage, error handling, and safety. It is fully self-contained and leaves no ambiguity about what the tool does or how to use it.

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% with a clear parameter description. The description adds value by showing the typical input format, expected output structure, and error format, which goes beyond the schema's definition. However, the schema already adequately describes the parameter, so a slight premium is given for the added context.

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 clearly states the tool checks a post against every major platform's length limit at once, listing specific platforms (X, LinkedIn, Instagram, Threads, YouTube, meta). This distinguishes it from siblings like analyze_writing and reading_time, which have different purposes.

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?

Explicitly says 'Use before posting, to catch truncation' and provides when-not-to-use: 'Not for readability (analyze_writing) and not for reading duration (reading_time).' This gives clear guidance on selection vs alternatives.

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