letta-ai/letta-code/generating-mod-envs

Generating mod learning envs

Use this skill to create JSON envs consumed by /mods learn --env=<path> or bun scripts/mod-learning/learn-mod.ts --env <path>. An env describes the mod behavior to learn and the scenario-suite eval used to score candidates.

Workflow

1. Define the behavior and eval before writing JSON.

• What should the mod do? Tool, turn event, tool event, provider, command, status, etc.
• What would a placebo/no-op mod fail?
• What unique sentinel strings make success unambiguous?

1. Choose a path:

• Repo example: docs/examples/mods/learning/<slug>.env.json
• Local/private: any user-requested path

1. Draft strict JSON. Start from assets/mod-learning-env.template.json if useful. No comments or trailing commas.
2. Prefer evaluation.scenarios with at least:

• happy path
• discrimination/exact-target path
• negative control

1. Validate:

bun src/skills/builtin/generating-mod-envs/scripts/validate-mod-env.ts path/to/env.json

If this skill is installed outside the source tree, run the same script from this skill directory: scripts/validate-mod-env.ts.

1. If asked to run it:

/mods learn --env=path/to/env.json --model=auto --backend=api --out=/tmp/<slug>-learn

The raw scripts/mod-learning/learn-mod.ts dev script detaches by default. Add --foreground only when a blocking pass/fail exit code is needed.

Use single-line --flag=value commands for TUI instructions.

Env shape

Required top-level fields:

• name: human display name.
• slug: stable kebab-case run/candidate slug.
• objective: one-paragraph target for the generation agent.
• requirements: concrete pass/fail behavior constraints.
• evaluation: either a single prompt eval or a scenario suite.

Common optional fields:

• targetModName: display metadata for the intended mod filename. The harness still chooses the candidate filename from slug unless --candidate-file-name is passed.
• candidateDiversityHints: strategies assigned across multi-candidate runs.
• modApiHints: concise API reminders that prevent bad generated code.
• examples: small input/expected demos for the generation prompt.

Evaluation fields:

• evaluation.outputFormat: use stream-json when checking trace markers.
• evaluation.timeoutMs, evaluation.maxTurns: per-scenario defaults.
• evaluation.memoryFiles: files seeded under eval $MEMORY_DIR.
• evaluation.scenarios[]: scenario-specific overrides and fixtures.
• In scenario-suite envs, do not add a top-level evaluation.prompt unless that prompt must run for every scenario. Assertion-only scenarios should have assertions and no prompt; only scenarios that require model behavior should define scenario.prompt.
• requiredResultMarkers: literal strings required in the final answer.
• requiredTraceMarkers: literal strings required in raw stdout/stderr.
• forbiddenResultMarkers: final-answer strings that fail the run.
• forbiddenTraceMarkers: raw trace strings that fail the run.

Quality rules

• Design the eval first. A useful env distinguishes success from a no-op mod.
• Use unique sentinels, e.g. MY-MOD-CANARY-OK, not common phrases.
• Seed memoryFiles rather than depending on real user memory or repo files.
• Include negative controls for non-use. If behavior should be conditional, verify it stays silent when not triggered.
• Include discrimination scenarios when paths, IDs, or sources matter. Put a tempting wrong sentinel in an irrelevant fixture and forbid it in the final answer.
• Put load failures in forbiddenTraceMarkers, usually:
• [mods] failed to load
• [extensions] failed to load
• loaded 0 mod(s)
• loaded 0 extension(s)
• For eval-facing tools, require requiresApproval: false, parallelSafe: true, and a strict no-argument schema when applicable.
• Avoid over-brittle trace markers. Prefer stable substrings like the tool name plus "message_type":"tool_return_message".
• Keep requirements behavioral; put fragile implementation details in modApiHints only when needed.

Minimal scenario-suite example

{
  "name": "Hello tool mod learner demo",
  "slug": "hello-tool",
  "objective": "Learn a trusted local mod that registers a read-only hello_mod_ping tool returning a fixed sentinel.",
  "requirements": [
    "Register a tool named hello_mod_ping.",
    "The tool must accept no parameters, require no approval, be parallelSafe, and return the exact string HELLO-MOD-OK."
  ],
  "candidateDiversityHints": [
    "Use the smallest possible tool-only implementation.",
    "Add explicit defensive checks around the tool schema."
  ],
  "modApiHints": [
    "Use export function activate(letta) or a default export.",
    "Use letta.tools.register({ name, description, parameters, requiresApproval, parallelSafe, run }).",
    "A no-argument tool schema is { \"type\": \"object\", \"properties\": {}, \"additionalProperties\": false }."
  ],
  "evaluation": {
    "outputFormat": "stream-json",
    "timeoutMs": 900000,
    "maxTurns": 6,
    "forbiddenTraceMarkers": ["[mods] failed to load", "loaded 0 mod(s)"],
    "scenarios": [
      {
        "name": "happy-path",
        "prompt": "Call the hello_mod_ping tool, then answer with the exact text HELLO-MOD-OK.",
        "requiredResultMarkers": ["HELLO-MOD-OK"],
        "requiredTraceMarkers": ["hello_mod_ping", "\"message_type\":\"tool_return_message\""]
      },
      {
        "name": "negative-control",
        "prompt": "Answer without calling tools: what is 2 + 2?",
        "requiredResultMarkers": ["4"],
        "forbiddenTraceMarkers": ["hello_mod_ping"]
      }
    ]
  }
}