set_env

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

No annotations are provided, so the description carries the disclosure burden. It usefully states that the variable is session-scoped, implying non-persistence across sessions, but it does not mention whether existing variables are overwritten, what happens after the session ends, or any affect on subprocesses.

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 a single short sentence with no filler. It front-loads the action and includes the most important qualifier, 'for this session,' without wasting words.

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, the description covers the core purpose and scope. Missing details like return value or overwrite behavior are minor for this tool type, and no output schema exists to demand additional return-format explanation.

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%, so the parameters are already documented in the input schema. The description adds no additional meaning about variable naming rules, value format, or how the value is interpreted.

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 verb (set), resource (environment variable), and scope (this session), making the tool's basic purpose evident. It inherently distinguishes from the sibling get_env through the set/get opposition, though it doesn't explicitly name the alternative.

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 this session' implies a session-bound context, but the description provides no explicit guidance on when to use this tool versus alternatives like get_env or memory_store. There are no exclusions, prerequisites, or stated conditions.

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