Built-in, Liquid-compatible filter library. Zero runtime dependencies — everything below uses only Elixir/OTP stdlib.

Two intentional deviations from a literal reading of issue 1.4.3, both for correctness against real Liquid semantics:

• url_encode / url_decode use URI.encode_www_form/1 / URI.decode_www_form/1 (space becomes +), not URI.encode/1 / URI.decode/1 — the latter percent-encodes spaces as %20 and doesn't match Liquid's actual url_encode output.
• ceil / floor return integers (trunc(Float.ceil(x))), matching Liquid, rather than Float.ceil/1's own float return value.

join with no argument defaults to "" (empty separator) per issue 1.4.3's explicit instruction, not Liquid's own default of " " — flagged here since it is a real behavioral divergence from upstream Liquid.

Type coercion reference

Every filter clause below is a private apply_builtin/3 head, so none of them can carry their own @doc (the compiler warns — @doc has no effect on a private function). This table is the substitute: it's the single place documenting what each filter does when handed a value of the "wrong" type, instead of that behavior being scattered implicitly across 56 private function clauses.

Coerces to a string (coerce_to_string/1)

upcase, downcase, capitalize, strip, lstrip, rstrip, strip_newlines, prepend, append, replace, replace_first, remove, remove_first, split, truncate, truncatewords, newline_to_br, escape, escape_once, strip_html, url_encode, url_decode, base64_encode, base64_decode, sort_natural (for comparison only — the original items are returned), join's separator argument (not its items). nil coerces to ""; numbers and booleans coerce via Integer.to_string/1 / Float.to_string/1 / to_string/1; anything else falls back to inspect/1 rather than raising.

slice also coerces its input via coerce_to_string/1 — unlike upstream Liquid, it does not support slicing arrays, only strings (see COMPATIBILITY.md).

Coerces to a number (coerce_to_number/1)

abs, ceil, floor, round, plus, minus, times, divided_by, modulo, at_least, at_most. nil coerces to 0, true/false to 1/0, and a numeric string parses to an integer or float; a non-numeric string or any other type coerces to 0 rather than raising.

No coercion — requires an exact type

• size — matches only on is_binary/is_list guards; any other input falls through to the catch-all clause and returns {:error, {:invalid_filter_args, "size", args}}, not a crash.
• first, last, reverse, sort, uniq, compact, map, where, concat, push, pop, unshift, shift, flatten — all expect a list; a non-list input raises (FunctionClauseError or Protocol.UndefinedError), the same as calling the underlying List/Enum function directly with that value.
• date — accepts a Date/DateTime/NaiveDateTime struct or an ISO 8601 string; anything else returns {:error, {:invalid_date, value}}, not a crash.
• default — no coercion; blankness is an exact-value check against nil, false, "", and [] (see blank?/1), not a truthiness rule.
• inspect — accepts any term as-is via Kernel.inspect/1; there is nothing to coerce.