CEL Functions

Functions available in Telo CEL expressions (!cel "..." tags and the ${{ }} holes of !interpolate). This page is generated from the runtime registry, so it matches what the kernel actually provides. Locally, telo cel functions prints the same list and telo cel eval "<expr>" evaluates an expression.

non-deterministic functions re-evaluate per call (in an x-telo-eval: compile field they bake once at load, which telo check warns about). host functions need the kernel's host handlers (Node crypto / Buffer).

Call form

A signature's shape is how you must call it. upper(string): string is a global function — upper(name); string.startsWith(string): bool is a method on its receiver — name.startsWith('x'). Writing one as the other does not type-check, and no cast repairs it. Some names exist in both forms (trim, split, size, join), some in only one.

Telo's own functions below are global. CEL's built-ins are mostly methods and are listed at the end — they were previously absent from this page entirely, which is why calling them globally was such a common mistake.

CEL has no assignment or statements. Reuse a subexpression with the cel.bind(name, init, expr) macro, and use default(value, fallback) / optional access (x.?field.orValue(d)) where you'd reach for ??.

Collections

Signature	Description
join(list, string): string	Join list elements into a string with a separator.
keys(map): list	List a map's keys.
values(map): list	List a map's values.
distinct(list): list	Remove duplicate elements, preserving order.
reverse(list): list	Reverse a list (copy; never mutates the input).
flatten(list): list	Flatten one level of nested lists.
sort(list): list	Sort a list numerically (numbers) or lexicographically; copy.
range(int): list<int>	Integers [0, n-1] (empty for n <= 0); materializes indices for an unknown-length list.
enumerate(list): list	Pair each element with its zero-based position as {index, value}.
slice(dyn, int, int): dyn	Take the half-open range [start, end) of a string, bytes or list.
compact(dyn): dyn	Drop entries whose value is null or the empty string, from a map or a list.
merge(map, map): map	Combine two maps, with the right-hand map winning on a shared key. Use it to add to a map rather than replace it — merge(defaults, overrides).

Strings

Signature	Description
lower(string): string	Lowercase a string.
upper(string): string	Uppercase a string.
trim(string): string	Strip leading/trailing whitespace.
replace(string, string, string): string	Replace all occurrences of a substring.
split(string, string): list	Split a string on a separator into a list.
regexReplace(string, string, string, string?): string	Replace every regex match (RE2 syntax) with a replacement ($1 backrefs); flags like 'i', 'm', 's'.
regexExtract(string, string, string?): string	First whole match of a regex (RE2 syntax), or '' when there is none.
regexExtractAll(string, string, string?): list<string>	Every whole match of a regex (RE2 syntax), in order.
regexGroups(string, string, string?): list<string>	Capture groups of the first regex match (RE2 syntax); empty list when there is no match.
trimPrefix(string, string): string	Strip a leading prefix if present.
trimSuffix(string, string): string	Strip a trailing suffix if present.
string.joinPath(string): string	Join a relative path onto a path with the host's separator (\ on Windows). On a host path it yields a host path; an absolute argument is refused. (host)

Math

Signature	Description
abs(dyn): double	Absolute value.
floor(dyn): double	Round down to an integer.
ceil(dyn): double	Round up to an integer.
round(dyn, int?): double	Round to the nearest integer, or to the given number of decimal places (0–10). The two-argument form shares the formatter's rounding rule, so a rounded value and the cell rendered beside it agree at the boundary. An integer past 2^53 is refused rather than rounded to a neighbour.
min(list): dyn	Smallest element (by numeric value); null for an empty list.
max(list): dyn	Largest element (by numeric value); null for an empty list.
sum(list): double	Sum of a list's numeric elements; 0 for an empty list.
avg(list): dyn	Arithmetic mean of a list's numeric elements; null for an empty list.

JSON

Signature	Description
json(dyn): string	Serialize any value to a JSON string. (host)
parseJson(string): dyn	Parse a JSON string into a value (numbers come back as doubles).

Encoding

Signature	Description
base64Encode(string): string	Encode a UTF-8 string as base64. (host)
base64Decode(string): string	Decode a base64 string to UTF-8. (host)
bytesFromBase64(string): bytes	Decode a base64 string to raw bytes.
bytesToBase64(bytes): string	Encode raw bytes as a base64 string.
urlEncode(string): string	Percent-encode a URI component.
urlDecode(string): string	Decode a percent-encoded URI component.

Hashing

Signature	Description
sha256(string): string	SHA-256 hash, hex-encoded. (host)
md5(string): string	MD5 hash, hex-encoded. (host)
sha1(string): string	SHA-1 hash, hex-encoded. (host)
sha512(string): string	SHA-512 hash, hex-encoded. (host)
hmac(string, string, string): string	HMAC of message under key for an algorithm (e.g. 'sha256'), hex. (host)

Null handling

Signature	Description
default(dyn, dyn): dyn	Return the value, or the fallback when it is null.
coalesce(list): dyn	First non-null element of a list, or null.

Time

Signature	Description
now(): timestamp	Current instant as a native timestamp, for comparison and duration arithmetic. (non-deterministic)
nowIso(string?): string	Current time as ISO-8601; UTC by default, or in the given IANA timezone. (non-deterministic)
today(string?): string	Current calendar date (YYYY-MM-DD); UTC by default, or in the given IANA timezone. (non-deterministic)
nowMillis(): int	Current time as epoch milliseconds (absolute; timezone-independent). (non-deterministic)
nowSeconds(): int	Current time as epoch seconds (absolute; timezone-independent). (non-deterministic)
dateIn(timestamp, string?): string	Calendar date (YYYY-MM-DD) of an instant, in an IANA zone (UTC by default).
isoIn(timestamp, string?): string	ISO-8601 rendering of an instant, in an IANA zone (UTC by default).
startOfMonth(timestamp, string?): timestamp	Midnight on the 1st of the instant's month, in an IANA zone (UTC by default).
addMonths(timestamp, int, string?): timestamp	Shift an instant by whole months in an IANA zone, clamping the day of month (Jan 31 + 1 month is Feb 28).

Formatting

Signature	Description
format(dyn, string): string	Format a number with a d3-format specifier (.2f, ,.2f, .1%, .2s).
fixed(dyn, int): string	Fixed-decimal string with the given number of places (0–10).
formatDuration(dyn, int): string	Render a minute count against a declared day length: formatDuration(510, 480) is 1d 30m. The day length is an argument because it is a policy, not arithmetic. The result is a rendering for a reader, not a duration literal — its d is the declared day, so it must not be fed back into a field that parses a duration.

UUID

Signature	Description
uuidv1(): string	Time-based UUID (v1). (non-deterministic)
uuidv4(): string	Random UUID (v4). (non-deterministic)
uuidv6(): string	Time-ordered UUID (v6). (non-deterministic)
uuidv7(): string	Time-ordered UUID (v7). (non-deterministic)
uuidv3(string, string): string	Name-based UUID (v3, MD5) under a namespace UUID.
uuidv5(string, string): string	Name-based UUID (v5, SHA-1) under a namespace UUID.
uuidValidate(string): bool	True if the string is a valid UUID.
uuidVersion(string): int	The version number of a UUID.

CEL built-ins

Provided by CEL itself, grouped by what they are called on.

Global functions

• !(bool): bool
• !=(bool, bool): bool
• !=(bytes, bytes): bool
• !=(double, double): bool
• !=(google.protobuf.Duration, google.protobuf.Duration): bool
• !=(google.protobuf.Timestamp, google.protobuf.Timestamp): bool
• !=(int, int): bool
• !=(list<A>, list<A>): bool
• !=(map<K, V>, map<K, V>): bool
• !=(null, null): bool
• !=(optional<A>, optional<A>): bool
• !=(string, string): bool
• !=(type, type): bool
• !=(uint, uint): bool
• %(int, int): int
• %(uint, uint): uint
• *(double, double): double
• *(int, int): int
• *(uint, uint): uint
• +(bytes, bytes): bytes
• +(double, double): double
• +(google.protobuf.Duration, google.protobuf.Duration): google.protobuf.Duration
• +(google.protobuf.Duration, google.protobuf.Timestamp): google.protobuf.Timestamp
• +(google.protobuf.Timestamp, google.protobuf.Duration): google.protobuf.Timestamp
• +(int, int): int
• +(list<A>, list<A>): list<A>
• +(string, string): string
• +(uint, uint): uint
• -(double): double
• -(double, double): double
• -(google.protobuf.Duration, google.protobuf.Duration): google.protobuf.Duration
• -(google.protobuf.Timestamp, google.protobuf.Duration): google.protobuf.Timestamp
• -(google.protobuf.Timestamp, google.protobuf.Timestamp): google.protobuf.Duration
• -(int): int
• -(int, int): int
• -(uint, uint): uint
• /(double, double): double
• /(int, int): int
• /(uint, uint): uint
• <(bool, bool): bool
• <(bytes, bytes): bool
• <(double, double): bool
• <(double, int): bool
• <(double, uint): bool
• <(google.protobuf.Duration, google.protobuf.Duration): bool
• <(google.protobuf.Timestamp, google.protobuf.Timestamp): bool
• <(int, double): bool
• <(int, int): bool
• <(int, uint): bool
• <(string, string): bool
• <(uint, double): bool
• <(uint, int): bool
• <(uint, uint): bool
• <=(bool, bool): bool
• <=(bytes, bytes): bool
• <=(double, double): bool
• <=(double, int): bool
• <=(double, uint): bool
• <=(google.protobuf.Duration, google.protobuf.Duration): bool
• <=(google.protobuf.Timestamp, google.protobuf.Timestamp): bool
• <=(int, double): bool
• <=(int, int): bool
• <=(int, uint): bool
• <=(string, string): bool
• <=(uint, double): bool
• <=(uint, int): bool
• <=(uint, uint): bool
• ==(bool, bool): bool
• ==(bytes, bytes): bool
• ==(double, double): bool
• ==(google.protobuf.Duration, google.protobuf.Duration): bool
• ==(google.protobuf.Timestamp, google.protobuf.Timestamp): bool
• ==(int, int): bool
• ==(list<A>, list<A>): bool
• ==(map<K, V>, map<K, V>): bool
• ==(null, null): bool
• ==(optional<A>, optional<A>): bool
• ==(string, string): bool
• ==(type, type): bool
• ==(uint, uint): bool
• >(bool, bool): bool
• >(bytes, bytes): bool
• >(double, double): bool
• >(double, int): bool
• >(double, uint): bool
• >(google.protobuf.Duration, google.protobuf.Duration): bool
• >(google.protobuf.Timestamp, google.protobuf.Timestamp): bool
• >(int, double): bool
• >(int, int): bool
• >(int, uint): bool
• >(string, string): bool
• >(uint, double): bool
• >(uint, int): bool
• >(uint, uint): bool
• >=(bool, bool): bool
• >=(bytes, bytes): bool
• >=(double, double): bool
• >=(double, int): bool
• >=(double, uint): bool
• >=(google.protobuf.Duration, google.protobuf.Duration): bool
• >=(google.protobuf.Timestamp, google.protobuf.Timestamp): bool
• >=(int, double): bool
• >=(int, int): bool
• >=(int, uint): bool
• >=(string, string): bool
• >=(uint, double): bool
• >=(uint, int): bool
• >=(uint, uint): bool
• bool(bool): bool
• bool(string): bool
• bytes(bytes): bytes
• bytes(string): bytes
• double(double): double
• double(int): double
• double(string): double
• double(uint): double
• duration(google.protobuf.Duration): google.protobuf.Duration
• duration(string): google.protobuf.Duration
• dyn(A): dyn
• in(A, list<A>): bool
• in(K, map<K, V>): bool
• int(double): int
• int(google.protobuf.Duration): int
• int(google.protobuf.Timestamp): int
• int(int): int
• int(string): int
• int(uint): int
• matches(string, string): bool
• size(bytes): int
• size(list<A>): int
• size(map<K, V>): int
• size(string): int
• string(bool): string
• string(bytes): string
• string(double): string
• string(google.protobuf.Duration): string
• string(google.protobuf.Timestamp): string
• string(int): string
• string(string): string
• string(uint): string
• timestamp(google.protobuf.Timestamp): google.protobuf.Timestamp
• timestamp(int): google.protobuf.Timestamp
• timestamp(string): google.protobuf.Timestamp
• type(bool): type
• type(bytes): type
• type(double): type
• type(google.protobuf.Duration): type
• type(google.protobuf.Timestamp): type
• type(int): type
• type(list<A>): type
• type(map<K, V>): type
• type(null): type
• type(optional<A>): type
• type(string): type
• type(type): type
• type(uint): type
• uint(double): uint
• uint(int): uint
• uint(string): uint
• uint(uint): uint

On bytes

• bytes.at(int): int
• bytes.base64(): string
• bytes.hex(): string
• bytes.json(): dyn
• bytes.size(): int
• bytes.string(): string

On google.protobuf.Duration

• google.protobuf.Duration.getHours(): int
• google.protobuf.Duration.getMilliseconds(): int
• google.protobuf.Duration.getMinutes(): int
• google.protobuf.Duration.getSeconds(): int

On google.protobuf.Timestamp

• google.protobuf.Timestamp.getDate(): int
• google.protobuf.Timestamp.getDate(string): int
• google.protobuf.Timestamp.getDayOfMonth(): int
• google.protobuf.Timestamp.getDayOfMonth(string): int
• google.protobuf.Timestamp.getDayOfWeek(): int
• google.protobuf.Timestamp.getDayOfWeek(string): int
• google.protobuf.Timestamp.getDayOfYear(): int
• google.protobuf.Timestamp.getDayOfYear(string): int
• google.protobuf.Timestamp.getFullYear(): int
• google.protobuf.Timestamp.getFullYear(string): int
• google.protobuf.Timestamp.getHours(): int
• google.protobuf.Timestamp.getHours(string): int
• google.protobuf.Timestamp.getMilliseconds(): int
• google.protobuf.Timestamp.getMilliseconds(string): int
• google.protobuf.Timestamp.getMinutes(): int
• google.protobuf.Timestamp.getMinutes(string): int
• google.protobuf.Timestamp.getMonth(): int
• google.protobuf.Timestamp.getMonth(string): int
• google.protobuf.Timestamp.getSeconds(): int
• google.protobuf.Timestamp.getSeconds(string): int

On list<A>

• list<A>.size(): int

On list<string>

• list<string>.join(): string
• list<string>.join(string): string

On map<K, V>

• map<K, V>.size(): int

On optional<A>

• optional<A>.hasValue(): bool
• optional<A>.or(optional<A>): optional<A>
• optional<A>.orValue(A): A
• optional<A>.value(): A

On string

• string.contains(string): bool
• string.endsWith(string): bool
• string.indexOf(string): int
• string.indexOf(string, int): int
• string.lastIndexOf(string): int
• string.lastIndexOf(string, int): int
• string.lowerAscii(): string
• string.matches(string): bool
• string.size(): int
• string.split(string): list<string>
• string.split(string, int): list<string>
• string.startsWith(string): bool
• string.substring(int): string
• string.substring(int, int): string
• string.trim(): string
• string.upperAscii(): string