Reactivity creates feedback loops between creator and reader, between content and context. Where updatability focuses on how authors change work over time, reactivity emphasizes how work responds to readers, adapting its presentation or behavior based on user interaction, input, or environmental conditions. The counter to reactivity is fixed form, where the work presents identically regardless of who encounters it or how they interact with it.

Reactivity differs fundamentally from updatability. While updatability concerns the content itself changing, reactivity focuses on the framework or display adapting to receive and respond to input. A reactive system learns, adjusts, reorganizes, or customizes based on feedback. This can happen at different timescales: immediate reactivity occurs when a user can filter content or decide what to display right now, and the work responds instantly. Learning reactivity happens when the work can grow and learn over longer timeframes, observing user behaviors and changing the order or emphasis of content accordingly.

The question of who initiates the reaction matters. Is the framework reactive to the user's explicit choices (clicking, filtering, customizing), or does it react to passive behaviors (reading patterns, dwell time, collective usage data)? What kind of feedback does the work accept? Explicit input through forms and filters? Behavioral data from how readers navigate? Environmental sensors detecting context?

How does the work respond? Does it reorganize content, customize presentation, generate new material, or adapt its structure? Is the response immediate or gradual? Does the work react in real time to individual interactions, or does it learn patterns over time and adapt accordingly? Can reactivity be disabled? Can readers choose to experience a "fixed" version, or is reactivity fundamental to accessing the work?

Cyberfeminism Index enables readers to filter and explore the archive through multiple pathways, with each reader potentially discovering entirely different connections based on their navigation choices. Responsive web design adapts presentation to screen size, device capabilities, and user preferences. The content may stay the same, but the framework reacts to context.

A Party to Print creates reactive feedback by capturing party interactions as content. The book reacts to and records the behaviors of participants. Performers responding to audiences create reactive feedback loops in real time. The performer can answer questions, adjust pacing, and emphasize different aspects based on audience response. The same content becomes a different experience each time.

Databases with sorting and filtering represent the most common form of reactivity. A catalog or index that lets viewers reorganize content through different criteria allows readers to reconstruct the work through their own understanding and interests. Recommendation systems adapt content presentation based on past interactions, collective usage patterns, or declared preferences. The work reorganizes itself reactively. Form adapting installations in gallery spaces that change based on viewer proximity, sound levels, or environmental conditions demonstrate physical reactivity.

Projects exploring reactivity employ explicit filtering that gives readers controls to sort, filter, or customize content presentation based on their interests and needs. Behavioral adaptation tracks (with consent) how readers navigate and adjusts emphasis, order, or suggested connections accordingly. Collective shaping allows aggregate reader behaviors to influence how work presents to future readers, creating evolving collective experiences. Environmental response creates work that reacts to time of day, location, weather, or other contextual factors. Accessibility customization enables readers to adjust typography, contrast, layout, or content density for accessibility. Generative response builds systems that generate new content or variations based on interaction patterns. Feedback visualization makes the reactive process visible so readers can see how their interactions shape the work.