set_session_variable

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

Annotations already carry the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), and the description is consistent with them — no contradiction. The description adds persistence-across-calls context but does not disclose overwrite semantics (does re-setting an existing name replace or error?), name constraints, or whether variables survive beyond the current session.

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?

A single 12-word sentence with the verb and resource front-loaded and zero filler. Every word earns its place; nothing is redundant or padded.

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 two-parameter setter with full schema coverage and safety annotations, the combined description, schema, and annotations are nearly sufficient for an agent to invoke it correctly. Minor gaps remain around overwrite behavior and session-lifetime semantics, but nothing critical is missing.

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 description coverage is 100% — both 'name' ('Variable name') and 'value' ('Variable value (string, number, boolean, array, or object)') are documented inline with type information. The description adds no parameter detail beyond the schema, so the 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?

The description uses a specific action verb ('Set') with a precise resource ('user-defined session variable') and states the purpose ('for use across tool calls'). 'User-defined' distinguishes it from system session context, and the verb alone differentiates it from siblings like get_session_variable and delete_session_variable.

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?

The phrase 'for use across tool calls' implies the core scenario — persisting state between calls — but no explicit when/when-not guidance or alternative routing is given. Given the rich session-tool family (get_session_variable, delete_session_variable, get_session_context, clear_session_context, list_session_history), explicit differentiation would help.

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