Aider-AI/aider · error · UnknownEditFormat

Unknown edit format {edit_format}. Valid formats are: {', '.

Error message

Unknown edit format {edit_format}. Valid formats are: {', '.join(valid_formats)}

What it means

Thrown by Coder.create() when the requested edit_format string does not match the edit_format attribute of any coder class registered in coders.__all__. The error message enumerates all valid formats collected from the registered coders. It is the top-level factory guard: no coder backend can be constructed for an unknown format name.

Source

Thrown at aider/coders/base_coder.py:201

            )
            use_kwargs.update(update)  # override to complete the switch
            use_kwargs.update(kwargs)  # override passed kwargs

            kwargs = use_kwargs
            from_coder.ok_to_warm_cache = False

        for coder in coders.__all__:
            if hasattr(coder, "edit_format") and coder.edit_format == edit_format:
                res = coder(main_model, io, **kwargs)
                res.original_kwargs = dict(kwargs)
                return res

        valid_formats = [
            str(c.edit_format)
            for c in coders.__all__
            if hasattr(c, "edit_format") and c.edit_format is not None
        ]
        raise UnknownEditFormat(edit_format, valid_formats)

    def clone(self, **kwargs):
        new_coder = Coder.create(from_coder=self, **kwargs)
        return new_coder

    def get_announcements(self):
        lines = []
        lines.append(f"Aider v{__version__}")

        # Model
        main_model = self.main_model
        weak_model = main_model.weak_model

        if weak_model is not main_model:
            prefix = "Main model"
        else:
            prefix = "Model"

View on GitHub (pinned to 5dc9490bb3)

Solutions

1. Read the error text: it prints the exact valid_formats list for your installed version; use one of those strings verbatim.
2. Check for typos/case: matching is exact string equality (e.g. 'editblock' vs the actual 'diff' naming used by your version).
3. Upgrade or align versions: if a script targets an older/newer aider, compare that version's coders/__init__.py export list to see which formats exist.
4. If you registered a custom coder, verify it is exported in coders.__all__ and has a non-None edit_format class attribute.

Example fix

# before
coder = Coder.create(main_model=model, io=io, edit_format="editblock")

# after
coder = Coder.create(main_model=model, io=io, edit_format="diff")  # use a value from the error's valid_formats list

from aider.coders import Coder

def valid_edit_formats():
    from aider import coders
    return {
        str(c.edit_format)
        for c in coders.__all__
        if hasattr(c, "edit_format") and c.edit_format is not None
    }

fmt = "diff"
assert fmt in valid_edit_formats(), f"bad edit_format {fmt!r}; pick from {valid_edit_formats()}"

def is_valid_edit_format(fmt: str) -> bool:
    from aider import coders
    return any(
        hasattr(c, "edit_format") and c.edit_format == fmt
        for c in coders.__all__
    )

from aider.coders import Coder
try:
    coder = Coder.create(main_model=model, io=io, edit_format=fmt)
except UnknownEditFormat as e:
    # e.edit_format and e.valid_formats carry the details
    print(f"bad format {e.edit_format}; valid: {e.valid_formats}")
    raise SystemExit(2)

When it happens

Trigger: Calling Coder.create(main_model, io, edit_format=...) (directly or via clone()/CLI --edit-format) with a string like 'diff', 'edit_block', or 'search-replace' that doesn't exactly equal a registered coder's edit_format (valid ones typically include 'whole', 'diff', 'diff-fenced', 'editor-diff', 'udiff', 'patch', 'ask'). Typos, case mismatches, and formats removed/renamed in newer aider versions all trigger it.

Common situations: Typo'd --edit-format CLI flag; scripts hard-coding an edit format that was renamed across aider versions; custom coder classes added to the package but missing the edit_format class attribute (they are silently skipped by the hasattr check); passing a model's name instead of the edit format.

Related errors

• Invalid line_endings value: {line_endings}. Must be one of:
• Error loading model settings from {model_settings_fname}: {e
• Error loading model definition from {model_fname}: {e}
• No data found in LLM response!
• # {len(failed)} SEARCH/REPLACE {blocks} failed to match!\n

AI-assisted analysis of Aider-AI/aider@5dc9490bb3 (2026-08-15). Data as JSON: /api/errors/9ffa543a78713258. Report an issue: GitHub.