Add or update environment variable

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

The description goes beyond the annotations by specifying the HTTP method (PUT) and the upsert behavior ('Add or update'), which aligns with idempotentHint=true. It does not disclose side effects like triggering service redeploys or required permissions, but annotations already cover the basic safety profile (readOnlyHint=false, destructiveHint=false).

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 two sentences, front-loaded with the core action. The first sentence is somewhat redundant with the title, but the second sentence meaningfully adds the endpoint. It is concise with no unnecessary details.

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, the schema fully documents parameters, and annotations indicate idempotency, the description is largely sufficient. It lacks mention of the return value (no output schema), but that is a minor gap for an upsert operation.

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 clear descriptions for all three parameters. The description references envGroupId and envVarKey in the endpoint path, which reinforces their roles, but it adds no meaning beyond the schema, particularly for the body variants (value vs generateValue).

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 adds or updates a specific environment variable within a specific environment group, which distinguishes it from sibling tools like render_update_env_var (generic) or render_update_env_vars_for_service. The inclusion of the exact PUT endpoint reinforces this precise scope.

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 description implies usage by clearly targeting 'a particular environment group', which is helpful context. However, it does not explicitly mention when NOT to use this tool or point to alternatives, such as using render_update_env_var for service-level variables or render_add_or_update_secret_file for secret files.

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