Tool Call Repair


ID	`tool_call_repair`
Category	Safety
Features	None
Dependencies	None
Risk	Low

Opt-in recovery net for malformed tool calls. Models occasionally emit tool-call arguments that are not clean JSON — wrapped in a Markdown code fence, surrounded by prose, with trailing commas or single quotes, or with values typed as strings where the schema wants numbers. Without repair, such a call either surfaces a parse error or silently collapses to empty arguments and fails downstream. This capability salvages the call so the turn proceeds.

Disabled by default. The capability is registered so agents can enable it, but contributes nothing unless explicitly selected. With it off, behavior is byte-for-byte unchanged.

Tools

None — the capability intercepts inside the reason step, after the model’s tool calls are finalized and before the assistant message is built.

How It Works

Deterministic local salvage — A pure function runs over each call’s arguments: it unwraps fenced code blocks and strips surrounding prose, removes trailing commas, normalizes single quotes to double quotes, and coerces string-typed known keys to the type declared by the tool’s JSON schema (e.g. "42" → 42 for an integer property). An already-valid call is a no-op.
Bounded corrective re-prompt — When local salvage cannot recover a usable object, the capability allows up to max_reprompts attempts per call (default
1. before falling through to the normal error path. The re-prompt is realized by the agent loop: the unrepaired call proceeds to today’s error path and the model retries on the next iteration. The per-call cap guarantees there is no infinite repair loop.
Observability — Each malformed call emits one tool.call_repaired event carrying an outcome label: local-salvage, re-prompt, or gave-up.

Configuration

Default

{
  "capabilities": ["tool_call_repair"]
}

Custom re-prompt cap

{
  "capabilities": [
    {
      "ref": "tool_call_repair",
      "config": { "max_reprompts": 2 }
    }
  ]
}

max_reprompts accepts 0–5. 0 means “salvage locally or fall straight through to the error path with no re-prompt”.

When To Enable

Use this capability when:

You run models or providers that occasionally wrap tool arguments in prose or code fences, or emit lenient JSON (single quotes, trailing commas)
You want a malformed call to recover the turn rather than waste an iteration on a raw parse error

Limitations

Verbatim JSON only: salvage extracts an embedded JSON object; it does not invent missing required fields or guess intent from natural language
Bounded input: argument blobs larger than 256 KiB are treated as un-salvageable without parsing (a denial-of-service guard against runaway model output)
No deep type checking: coercion handles top-level integer / number / boolean string values; full schema validation remains the tool’s job